Extend async override virtual call coverage

[Copilot]

Adds coverage for awaited virtual dispatch and generic virtual async overrides in src/tests/async/override/override.cs.

• Awaited virtual calls

  • Adds NoInlining helpers that await Base.M1() and Base1.M1().
  • Exercises both direct .Result virtual calls and awaited wrapper calls.

• Generic virtual async overrides

  • Adds M2<T>(T first, T second) across both override hierarchies.
  • Verifies dispatch returns:
    • empty list from base implementations
    • first argument from first-level overrides
    • second argument from second-level overrides

[MethodImpl(MethodImplOptions.NoInlining)]
static async Task<List<T>> AwaitBaseM2<T>(Base b, T first, T second) =>
    await b.M2(first, second);

[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

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[Copilot]

Pull request overview

This PR expands the src/tests/async/override/override.cs async-override test coverage by adding an awaited-call wrapper path and introducing a generic virtual async method (M2<T>) with overrides across two class hierarchies.

Changes:

• Add M2<T>(T first, T second) as a virtual async method on both Base and Base1, with overrides in derived types returning lists that reflect dispatch selection.
• Add [NoInlining] async helper wrappers that await virtual calls (AwaitBaseM1 / AwaitBaseM2) to exercise awaited virtual dispatch call sites.
• Extend assertions to validate both direct .Result calls and the awaited-wrapper paths for overridden implementations.