Fix command-line injection in grader process launch

[Copilot]

Addresses CodeQL alert #4 for uncontrolled command-line construction when launching the grader test executable. User-controlled values are now passed as discrete process arguments instead of being interpolated into a single command-line string.

• Process invocation
  • Replaced ProcessStartInfo.Arguments string interpolation with ProcessStartInfo.ArgumentList.
  • Preserves the existing executable, working directory, and argument order.

info.ArgumentList.Add(tempCredentialsFilePath);
info.ArgumentList.Add(tempDir);
info.ArgumentList.Add(trace);
info.ArgumentList.Add(filter);