release: prepare a3s-code 5.3.5

[ZhiXiao-Lin]

Summary

• preserve research workflow metadata and expose Bing RSS search
• defer session model validation for host-provided clients
• retry interrupted provider streams in the same turn without committing provisional output
• require protocol terminal evidence before emitting a final streaming response
• align Core, Node, Python, and bootstrap packages at 5.3.5

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --lib --bins -- -D warnings
• cargo test --workspace --locked (2438 tests)
• cargo test --workspace --all-features --lib --locked (2475 passed, 9 ignored)
• SemVer: 223/223 checks against 5.3.4
• SDK Rust checks, Node runtime/helper tests, TypeScript examples
• Core/Node/Python real-provider integration smokes
• Python bootstrap: 15 tests; wheel/sdist build and twine check
• clean git-archive with published dependencies: locked clippy/tests/package/publish --dry-run
• deterministic convergence benchmark: 4/4 cases