Add automated tests for conformance result utilities

[BHUVANSH855]

Description

The conformance package has two utilities for processing conformance result files:

• conformance/src/unexpected_fails.py
• conformance/src/validate_results.py

Neither currently has automated test coverage.

A coverage run of the conformance runner shows:

• unexpected_fails.py: 0% coverage (22 statements)
• validate_results.py: 0% coverage (62 statements)

Both utilities contain logic that would benefit from regression tests. unexpected_fails.py compares automated and manually recorded conformance results, while validate_results.py checks invariants in the generated TOML result files.

The existing result files currently pass both utilities:

• unexpected_fails.py reports no discrepancies.
• validate_results.py validates all 852 conformance result files without invariant violations.

Proposed change

Add focused automated tests covering the main behaviors of these utilities, including:

• matching automated and manual results
• detecting automated/manual result mismatches
• handling malformed TOML
• handling missing result keys
• accepting valid result files
• rejecting unknown result keys
• validating conformance_automated values
• validating conformant values
• handling missing conformant when appropriate
• requiring non-empty notes for partial conformance

This would provide regression coverage for the conformance result-processing utilities and make future changes to them safer.

Related: #1692