Implement internal PCCS

[ameba23]

This is intended to speed up verification.

Related issue: #27

Summary

• Added a Pccs collateral cache component and wired DCAP verification to use it instead of fetching collateral directly each time.
• Implemented cached collateral lookup plus explicit refresh behavior for stale entries.
• Updated attestation verifier construction to initialize and carry an internal Pccs instance.

Key changes

• Added new module: pccs.rs (/home/pumkin/src/flashbots/attested-tls-proxy/attested-tls/src/attestation/pccs.rs)
  • Pccs::get_collateral now returns (collateral, is_fresh) to indicate cache hit vs network fetch.
  • Pccs::refresh_collateral always refetches and overwrites cache.
• Updated DCAP flow in dcap.rs (/home/pumkin/src/flashbots/attested-tls-proxy/attested-tls/src/attestation/dcap.rs)
  • Uses Pccs for collateral retrieval.
  • Retries verification once with refreshed collateral only when the first attempt used cached collateral.
  • Avoids redundant second verification when first attempt already used fresh collateral.
• Updated verifier wiring in mod.rs (/home/pumkin/src/flashbots/attested-tls-proxy/attested-tls/src/attestation/mod.rs), plus call-site updates in main.rs (/home/pumkin/src/flashbots/
  attested-tls-proxy/src/main.rs) and lib.rs (/home/pumkin/src/flashbots/attested-tls-proxy/src/lib.rs).