Add test coverage for ref scoped modifier

[Copilot]

The grammar already supports scoped ref but lacked test coverage for the reverse order ref scoped, which is also valid C# syntax.

Changes:

• Added tests for ref scoped in method parameters and local variable declarations
• Extended grammar patterns to explicitly handle ref scoped in addition to scoped ref
• Updated capture groups to use dynamic modifier names for both readonly and scoped after ref

Example:

// Method parameter with ref scoped
public static Span<T> CreateSpan<T>(ref scoped T reference, int length) {}

// Local variable with ref scoped
ref scoped Span<int> x = stackalloc int[42];
ref scoped var y = ref z;

All 864 tests passing.

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