fix(mock-attestation): handle PCK collateral errors

[kvinwang]

Problem

The Rust checks workflow on master fails Clippy because the mock PCCS PCK CRL handler calls unwrap() while the workspace denies clippy::unwrap_used.

The panic is also inappropriate for an HTTP handler because collateral generation can fail.

Change

• handle sample_collateral() failures explicitly
• return HTTP 500 instead of panicking
• reuse the successfully generated collateral when setting the issuer-chain header

Verification

• cargo fmt --manifest-path dstack/Cargo.toml --all -- --check
• cargo clippy --manifest-path dstack/Cargo.toml -p mock-attestation -- -D warnings -D clippy::expect_used -D clippy::unwrap_used --allow unused_variables
• git diff --check

[Copilot]

🟢 Ready to approve

The change is small, localized to one handler, and brings behavior in line with existing error-handling patterns in this file while addressing the Clippy failure.

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Pull request overview

This PR updates the mock-attestation HTTP server to avoid unwrap() in the PCCS PCK CRL handler, aligning with the workspace’s Clippy clippy::unwrap_used denial and preventing panics in an HTTP request path.

Changes:

• Handle tdx.sample_collateral() failure in the PCK CRL route and return HTTP 500 instead of panicking.
• Reuse the generated collateral to populate the SGX-PCK-CRL-Issuer-Chain header (avoids regenerating collateral / second fallible call).

File summaries

File	Description
dstack/crates/mock-attestation/src/server.rs	Replaces unwrap() in the PCK CRL handler with explicit error handling and collateral reuse for the issuer-chain header.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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