Accept nullable generic class method rows in analyzer validation #7610

Summary

The TUnit0001 analyzer rejects integer method-source rows for nullable generic class parameters. Deliver the analyzer correction independently of discovery changes so supported tests compile without suppressing the diagnostic.

Proposal

Reuse the analyzer changes from branch issue-7573-nullable-analyzer at 36c8723ae14871d458537bdc8f3daf4dee479808. Own src/TUnit.Analyzers/Extensions/CompilationExtensions.cs, src/TUnit.Analyzers/TestDataAnalyzer.cs, and tests/TUnit.Analyzers.Tests/MethodDataSourceAnalyzerTests.cs. Do not copy generator, engine or STA snapshot changes.

Acceptance criteria

• Accept compatible int and int? method-source rows for T? on a class constrained with where T : struct.
• Preserve constraint diagnostics when method rows infer class types; honor explicit, constructor-inferred and inherited constructor types, including type-free constructor rows.
• Preserve existing last-occurrence inference behavior and cover uncertain and violating repeated-parameter cases in analyzer tests.
• Run affected method-data analyzer tests and the full analyzer suite. Keep unrelated TUnit0046 warning work in TUnit0046 warns about mutable references for nullable generic value-type rows #7598 and policy consolidation in Share class-row type inference between the source generator, analyzer and reflection #7377.
• There are no outstanding blocking analyzer findings on Fix nullable generic class method data source validation #7591; retain its reviewed analyzer regressions. This part can merge independently of the discovery part.

Parent: #7573. Split because #7591 exceeded the automated review budget.