test: add issue #357 regression coverage for complex C# enum values

[Widthdom]

Summary

• add issue C# enum members with complex constant-expression values (= K.Foo, = (int)1.5, = (1 + 2), = 'A', = System.Int32.MaxValue) are silently dropped — value-shape alternation accepts only \d / 0x / [A-Z]\w*\| #357 regression coverage for C# enum members that use complex constant expressions
• cover both extractor-level behavior and CLI end-to-end queries for symbols --exact-name and definition --exact-name
• document the regression coverage in the changelog

Notes

• current main already contains the runtime behavior; this PR pins that behavior with regression tests
• adversarial review reported no blocking/actionable findings

Closes #357