Fix sharedState data race in backgroundProposalOutcome

[brunotm]

This change fixes a unsynchronised access to outgen.sharedState.committedOutcome, by using the captured outctx.PreviousOutcome from the shared state which is passed by value to backgroundProposalOutcome.

Write at commit() at outcome_generation_follower.go:846 outgen.sharedState.committedOutcome = commit.Outcome

Read at backgroundProposalOutcome() at outcome_generation_follower.go:499 outgen.sharedState.committedOutcome when calling MakeOutcomeInputsDigest()

https://github.com/smartcontractkit/chainlink/actions/runs/22384997421/job/64793669658

==================
WARNING: DATA RACE
Write at 0x00c0339aade0 by goroutine 481858:
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).commit()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation_follower.go:846 +0x3ea
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).commit()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation_follower.go:842 +0x344
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).messageEpochStart()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation_follower.go:81 +0x14cb
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.MessageEpochStart[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }].processOutcomeGeneration()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/message.go:258 +0x150
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*MessageEpochStart[github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportInfo]).processOutcomeGeneration()
      <autogenerated>:1 +0x29
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).unbufferMessages()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation.go:273 +0x961
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).eventNewEpochStart()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation.go:349 +0x15f1
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.EventNewEpochStart[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }].processOutcomeGeneration()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/message.go:43 +0x6c
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*EventNewEpochStart[github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportInfo]).processOutcomeGeneration()
      <autogenerated>:1 +0x1b
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).run()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation.go:205 +0x885
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.RunOutcomeGeneration[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation.go:69 +0x3cc
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*oracleState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).run.func2()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/oracle.go:188 +0x4f1
  github.com/smartcontractkit/libocr/subprocesses.(*Subprocesses).Go.func1()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/subprocesses/subprocesses.go:29 +0x82

Previous read at 0x00c0339aade0 by goroutine 486328:
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).backgroundProposalOutcome()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation_follower.go:499 +0x1094
  github.com/smartcontractkit/libocr/offchainreporting2plus/internal/ocr3/protocol.(*outcomeGenerationState[go.shape.struct { LifeCycleStage github.com/smartcontractkit/chainlink-common/pkg/types/llo.LifeCycleStage; ReportFormat github.com/smartcontractkit/chainlink-common/pkg/types/llo.ReportFormat }]).tryProcessProposalPool.func1()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/offchainreporting2plus/internal/ocr3/protocol/outcome_generation_follower.go:383 +0x1d3
  github.com/smartcontractkit/libocr/subprocesses.(*Subprocesses).Go.func1()
      /home/runner/go/pkg/mod/github.com/smartcontractkit/libocr@v0.0.0-20260130195252-6e18e2a30acc/subprocesses/subprocesses.go:29 +0x82