GH2153: Fix async stack traces rendering as MoveNext() instead of source methods

[devlead]

• I have read the Contribution Guidelines
• I have checked that there isn't already another pull request that solves the above issue
• All newly added code is adequately covered by tests
• All existing tests are still running without errors

Changes

Async exception stack frames were showing async void MoveNext() because TryResolveStateMachineMethod took MethodBase by value. The resolved method (e.g. ExecuteAsync) was assigned to a local copy and never propagated back to the caller, matching .NET StackTrace behavior only partially.

• Pass MethodBase by ref in TryResolveStateMachineMethod and at its call site in GetMethodName
• Add async throw helpers to TestExceptions for regression coverage
• Add verifier test and snapshot asserting resolved async method names
• Fixes ExceptionRenderableBuilder shows async state machine methods (i.e. MoveNext) #2153

Example

catch(Exception exception)
{
    AnsiConsole.WriteException(
        exception,
        ExceptionFormats.ShortenEverything | ExceptionFormats.ShowLinks
    );
}

Before fix (broken — MethodBase passed by value)

InvalidOperationException: Throwing async!
  at async void MoveNext() in Exceptions.cs:100
  at void ThrowFromAsync() in Exceptions.cs:200
  at Exception GetException(Action action) in ExceptionTests.cs:300

After fix (ref MethodBase — matches .NET StackTrace)

InvalidOperationException: Throwing async!
  at async Task MethodThatThrowsAsync() in Exceptions.cs:100
  at void ThrowFromAsync() in Exceptions.cs:200
  at Exception GetException(Action action) in ExceptionTests.cs:300

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[patriksvensson]

Merged! Thank you for your contribution. Much appreciated! 👍