Add Capabilities Negotiations resp. missing fields

[sarroutbi]

This change enhances the capabilities negotiation phase of the push-attestation protocol by adding two timestamp fields to the verifier's response: capabilities_received_at and challenges_expire_at.

This change aligns the Rust data structures with the complete protocol specification, allowing the agent to correctly deserialize and process the time-sensitive information sent by the verifier.

ResponseAttributes Struct Updated: The ResponseAttributes struct in keylime/src/structures/capabilities_negotiation.rs has been modified to include two new optional fields:

• capabilities_received_at: Option<DateTime>: Records the exact time when the verifier processed the agent's initial capabilities request, establishing a baseline for the session.

• challenges_expire_at: Option<DateTime>: Specifies the deadline by which the agent must generate and submit its evidence.

• Unit Tests Updated: The serialization tests for AttestationResponse have been updated to include these new fields. This verifies that the Rust structs can correctly serialize and deserialize a JSON payload containing the new timestamps, ensuring compatibility with the verifier.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.52%. Comparing base (3c411a5) to head (d598a16).
Report is 1 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
e2e-testsuite	58.52% <ø> (-0.02%)	⬇️
upstream-unit-tests	58.52% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
keylime/src/structures/capabilities_negotiation.rs	75.00% <ø> (ø)

... and 3 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull Request Overview

Enhance the capabilities negotiation response by aligning the Rust structs with the protocol spec to include two new timestamps and updating tests to cover their serialization.

• Added capabilities_received_at and challenges_expire_at fields to ResponseAttributes
• Updated unit tests to include the new fields in JSON serialization/deserialization

Comments suppressed due to low confidence (2)

keylime/src/structures/capabilities_negotiation.rs:100

• [nitpick] Consider adding doc comments above these new fields to explain their purpose and usage according to the protocol specification.

    pub capabilities_received_at: Option<DateTime<Utc>>,

keylime/src/structures/capabilities_negotiation.rs:686

• Add tests for the case where these fields are None to verify that they are omitted in the serialized JSON and deserialized back as None.

                    capabilities_received_at: Some("2025-07-11T08:49:51.734539Z".parse().unwrap()), //#[allow_ci]