fix(enclave): reject malformed attestation quotes safely

[Alicepoltora]

Summary

The public evalAttestationEvidence JSON-RPC method passed attacker-controlled quote bytes directly to dcap-rs::QuoteV4::from_bytes. That parser is infallible and indexes variable-length fields directly, so malformed input could panic the enclave server and make attestation unavailable.

This change:

• validates the quote header, supported TEE type, body length, signature length, and truncation before parsing;
• catches malformed nested certification data from the current dcap-rs parser and returns a JSON-RPC error instead of panicking;
• adds regression tests for truncated, unsupported, undersized, and malformed quotes.

Verification

• cargo fmt --all --check
• cargo test -p seismic-enclave-server server::tests (6 passed)

The parser boundary is intentionally defensive because dcap-rs does not currently expose a fallible quote parser.