Fix TRX result attachment layout to include per-test relative results directory

[Copilot]

Bug Fix

What was the bug?

With --report-trx --results-directory TestResults, per-test artifacts were copied to .../In/<machine>/... while TRX consumers resolved attachments via .../In/<relativeResultsDirectory>/<machine>/.... This mismatch caused attachment open failures locally and dropped attachments in Azure DevOps publishing.

How did you fix it?

• Align per-test artifact copy path with TRX resolution semantics
  • Updated TrxReportEngine to route per-test artifact copies under:
    • <resultsDirectory>/<runDeploymentRoot>/In/<executionId>/<machineName>/...
  • executionId is already emitted as relativeResultsDirectory, so physical layout now matches downstream lookup behavior.
• Keep existing href behavior unchanged
  • ResultFile path remains machine-relative (<machineName>/<fileName>), preserving current TRX payload shape.
• Add focused regression coverage
  • Extended the existing TRX unit test to assert copy destination includes the relativeResultsDirectory segment.

string directoryName = relativeResultsDirectory is null
    ? Path.Combine(_configuration.GetTestResultDirectory(), runDeploymentRoot, "In", _environment.MachineName)
    : Path.Combine(_configuration.GetTestResultDirectory(), runDeploymentRoot, "In", relativeResultsDirectory, _environment.MachineName);

// per-test artifacts now pass executionId as relativeResultsDirectory
string href = CopyArtifactIntoTrxDirectoryAndReturnHrefValue(testFileArtifact.FileInfo, runDeploymentRoot, executionId);

Testing

Added/updated unit coverage in TrxTests to verify that per-test artifact copy paths include:
.../In/<relativeResultsDirectory>/MachineName/fileName.