Bump the full RustCrypto dependency tree to align with rand 0.10 and
rand_core 0.10. This resolves the split dependency graph where
ssh-key's transitive deps used signature v3 / elliptic-curve v0.14
while russh used the older stable versions.

Key dependency changes:
- signature 2.2 → 3.0.0-rc.10 (removes signature_next shim)
- elliptic-curve 0.13 → 0.14.0-rc.28, ecdsa 0.16 → 0.17.0-rc.16
- p256/p384/p521 0.13 → 0.14.0-rc.7
- ed25519-dalek 2.x → 3.0.0-pre.6 (add alloc feature for EncodePrivateKey)
- curve25519-dalek 4.x → 5.0.0-pre.6
- der 0.7 → 0.8, sec1 0.7 → 0.8, spki 0.7 → 0.8.0-rc.4
- pkcs8 0.10 → 0.11.0-rc.11, pkcs5 0.7 → 0.8.0-rc.13
- num-bigint pinned to git (PR Eugeny#338) for rand_0_10 feature

Code changes to match new APIs:
- OsRng removed in rand 0.10; replaced with rand::rng()
- PrivateKeyInfo/EncryptedPrivateKeyInfo now generic; use Ref aliases
- SecretKey::from_bytes → from_slice for ECDSA key construction
- FromEncodedPoint/ToEncodedPoint → FromSec1Point/ToSec1Point
- EphemeralSecret::random → generate_from_rng (Generate trait)
- RandBigInt → BigRng010, gen_biguint_range → random_biguint_range
- Remove duplicate Pkcs8Next error variant (now same pkcs8 version)

Temporary workarounds (with tracking comments):
- [patch.crates-io] hmac: git pin for digest 0.11.2 Clone regression
  (RustCrypto/MACs#254 merged, awaiting hmac 0.13.0-rc.6 release)
- num-bigint: git dep on PR Eugeny#338 branch for rand 0.10 support