Fix CI: stop workflow when build fails, skip artifact upload

[Copilot]

When rust-tests failed, the workflow continued to package and upload artifacts (coverage, bin.tar) that were never produced, causing misleading CI failures downstream.

Changes

• Removed continue-on-error: true from the rust-tests step in linux-build, macos-build, and windows-build jobs — default is already false
• Removed if: always() from post-build steps (upload coverage, prepare artifact, upload artifact) in all three jobs — these now only run on success
• Removed the "Fail if rust tests failed" step — was only needed as a workaround for the continue-on-error pattern; failures now naturally short-circuit the job

Before:

- name: Build and test with code coverage
  id: rust-tests
  continue-on-error: true        # allowed failure to propagate
  run: ./build.ps1 -Clippy -Test -CodeCoverage -ExcludePesterTests -Verbose
- name: Upload coverage data
  if: always()                   # ran even on build failure
  uses: actions/upload-artifact@v4

After:

- name: Build and test with code coverage
  id: rust-tests
  run: ./build.ps1 -Clippy -Test -CodeCoverage -ExcludePesterTests -Verbose
- name: Upload coverage data
  uses: actions/upload-artifact@v4

[github-actions]

Code Coverage Report

No Rust files were changed in this PR.

🔵 Full Codebase Coverage

81% (good)

Metric	Value
Total executable lines	18050
Lines covered by tests	14772
Coverage percentage	81%

Full codebase coverage measures all instrumented Rust lines across the project.

[Copilot]

Pull request overview

This PR updates the Rust GitHub Actions workflow to correctly short-circuit jobs when the build/test step fails, preventing downstream steps from attempting to package or upload artifacts that were never produced.

Changes:

• Removed continue-on-error: true from the rust-tests steps so failures stop the job normally.
• Removed if: always() from artifact/coverage upload and packaging steps so they only run on successful builds.
• Removed the explicit “Fail if rust tests failed” workaround step, since it’s no longer needed.