RUST-BUG-109: close ED2K callback and server parity gaps

[itlezy]

Summary

• close the ED2K callback and server state-machine gaps tracked by RUST-BUG-109
• adopt callback transports into live peer sessions with route-scoped, expiring authorization
• make bounded server packet failures request-local and preserve authenticated sessions
• retain LowID upload queue entitlement across direct-UDP and exact shared-server callbacks
• fence shared-server callback dispatch by endpoint, login generation, and current local HighID

Protocol evidence

Static comparison covered community eMule, aMule, ed2k-server-rust, maintained eMuleBB MFC behavior, and the Lugdunum 17.15 decompile. Stock/community wire behavior remains authoritative; maintained MFC improvements are retained where they strengthen admission or upload-grant preservation.

Validation

• cargo test -p emulebb-ed2k -p emulebb-core
  • 1,019 emulebb-ed2k unit tests
  • 394 emulebb-core unit tests
  • integration and doc tests
• cargo check -p emulebb-ed2k -p emulebb-core --all-targets
• cargo clippy -p emulebb-ed2k -p emulebb-core --all-targets -- -D warnings -A unfulfilled-lint-expectations -D clippy::allow_attributes
• cargo fmt --all -- --check
• git diff --check

[itlezy]

Tracking and closure documentation: emulebb/emulebb-tooling#8