Summary:

During JS bundle downloads from Metro, the multipart stream reader was copying each chunk into a new Buffer before passing it to listeners. For large bundles, this resulted in elevated peak memory usage due to duplicating chunk data (Okio read buffer + intermediate Buffer copy, plus downstream buffering), which can exceed emulator heap limits for large bundles.
Example: #52818
Repro: #52797

Changes

• Multipart parsing: pass a bounded BufferedSource per part (prevents reading past the part into the next boundary) and drain unread bytes after callbacks so listeners don’t need to fully consume the body.
• BundleDownloader: keep streaming download behavior while restoring atomic writes (.tmp + rename) to avoid partial bundles on interruption.
• Make Content-Type checks tolerant of parameters, parse X-Http-Status safely.

Changelog:

[ANDROID] [FIXED] - Reduced memory usage during JS bundle downloads by eliminating intermediate buffer copies

Test Plan:

• Verified multipart bundle downloads work correctly with progress callbacks displayed
• Verified non-multipart fallback path still functions
• Verified error responses are handled correctly
• Tested with large bundles (repro above) and confirmed reduced memory pressure and no crashes