Repeat Mpmc bounded buffer soak tests for fill-and-take scenarios

[Copilot]

The MPMC soak coverage was inconsistent: WhenAddIsContendedBufferCanBeFilled already ran 10 iterations, while the two concurrent fill-and-take scenarios ran once. This aligns those soak tests so the key buffer-fill contention paths execute with the same repetition.

• What changed

  • Converted WhileBufferIsFilledItemsCanBeTaken from a single-run [Fact] to a repeated [Theory]
  • Converted WhileBufferIsFilledCountCanBeTaken from a single-run [Fact] to a repeated [Theory]
  • Reused a shared SoakIterations constant so all three MPMC soak tests stay in sync
  • Added per-iteration output to the updated tests for parity with the existing contended-add soak test

• Result

  • The MPMC soak suite now exercises:
    • add contention
    • concurrent fill + take
    • concurrent fill + count
  • each for 10 iterations instead of only repeating the add-contention case

• Example

  [Theory]
  [Repeat(SoakIterations)]
  public async Task WhileBufferIsFilledItemsCanBeTaken(int iteration)
  {
      this.testOutputHelper.WriteLine($"Iteration {iteration}");
      // existing soak logic
  }

[coveralls]

coverage: 99.08% (-0.03%) from 99.11% — copilot/update-mpmc-bounded-buffer-tests into main