feat(migration): add Does.Match support and fix MSTest IsSameReferenceAs

[thomhurst]

Summary

• Add NUnit Does.Match and Does.Not.Match constraint support for migration
• Add Is.Matches to the with-message version in NUnit migration
• Fix MSTest migration to use correct method names IsSameReferenceAs and IsNotSameReferenceAs (was incorrectly using IsSameReference and IsNotSameReference)

Test plan

• All 102 NUnit migration tests pass
• All 32 MSTest migration tests pass
• All 42 xUnit migration tests pass (1 skipped for assembly attributes)

🤖 Generated with Claude Code

[thomhurst]

Summary

This PR adds support for NUnit's Does.Match and Does.Not.Match constraint migration and corrects MSTest's reference equality assertion names from IsSameReference/IsNotSameReference to IsSameReferenceAs/IsNotSameReferenceAs.

Critical Issues

None found ✅

Observations

1. Recent Revert Context

The latest commit on main (83744ec) is a revert of the exact feature this PR re-introduces. The revert message indicates that commit d7aa43d was problematic. Question: What issue caused the revert, and has this PR addressed it?

2. Code Quality

The changes are well-structured:

• MSTest migration properly uses IsSameReferenceAs/IsNotSameReferenceAs which matches the actual assertion names in TUnit.Assertions/Conditions/ReferenceEqualityAssertions.cs:10,47
• NUnit migration adds Does.Match → Matches and Does.Not.Match → DoesNotMatch conversions
• Test coverage includes both positive and negative cases for the new regex assertions
• The DoesNotMatch and Matches assertions exist in TUnit.Assertions/Conditions/StringAssertions.cs

3. TUnit Rules Compliance

• ✅ No dual-mode concerns (only migration code, not core engine)
• ✅ No source generator output changes
• ✅ No public API changes
• ✅ No reflection or AOT concerns
• ✅ Not in hot paths
• ✅ No VSTest dependencies

4. Test Coverage

The PR adds comprehensive test coverage:

• NUnit_Does_Not_EndWith_Converted (line 889)
• NUnit_Does_Match_Converted (line 927)
• NUnit_Does_Not_Match_Converted (line 965)

All tests follow the existing pattern and verify both the analyzer detection and code fix transformation.

Verdict

✅ APPROVE - No critical issues, but recommend understanding why the previous version was reverted to ensure those issues don't reoccur.