Centralize TLS parsing for inspection

[ryanfowler]

Summary

• Reuse the shared Rustls protocol-version helper in TLS inspection instead of duplicating min/max bound logic.
• Reuse the shared PEM and client-auth parsing helpers from src/tls/mod.rs for inspection CA material and client certificates.
• Keep inspection-specific custom verification in place so certificate display and OCSP capture behavior stay unchanged.
• Add a repository note in AGENTS.md so the shared TLS parsing boundary stays explicit.

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features tls::
• cargo test --all-features --test integration tls -- --test-threads=1