Split Viewer and Test builds into separate jobs in GHA to reduce potential for disk space exhaustion

[RyeMutt]

Description

Splits Viewer and Test builds into separate jobs in GHA to reduce potential for disk space exhaustion

Related Issues

Issue Link: #4677

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Additional Notes

[Copilot]

Pull request overview

This PR splits Viewer and Test builds into separate GitHub Actions matrix jobs to mitigate disk space exhaustion issues. The changes introduce a new build_variant matrix dimension with values Viewer and Tests, and modify the build script to handle test execution separately from viewer builds.

Key Changes

• Added a build_variant matrix dimension to create separate job instances for Viewer and Tests builds
• Modified build.sh to support a build_tests mode that only builds and runs tests, skipping viewer-specific build steps
• Adjusted artifact upload conditions to only run for Viewer builds, as test builds don't produce viewer artifacts

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/build.yaml	Added build_variant matrix dimension, updated environment variables to conditionally set build_viewer and build_tests, modified artifact upload conditions to only run for Viewer builds, updated cache keys to include build variant, removed macOS disk cleanup, and restricted Linux disk cleanup to Viewer builds only
build.sh	Added TESTING variable initialization, added conditional logic to check build_tests flag and set TESTING=ON, modified build() function to handle test builds separately with BUILD_AND_RUN_TESTS target, removed inline ctest execution from viewer build path

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[Copilot]

Adding the build_variant matrix dimension creates multiple build job instances for each runner/configuration combination. This causes downstream jobs (sign-and-package-windows, sign-and-package-mac, post-windows-symbols, post-mac-symbols) to have ambiguous dependencies since they use "needs: build" but there are now multiple build jobs (Viewer and Tests).

The downstream jobs will fail because GitHub Actions cannot determine which build job output to use. Consider either:

1. Adding a conditional to exclude the Tests variant from the matrix (e.g., using matrix.exclude)
2. Filtering downstream jobs to only run for the Viewer variant
3. Separating the build job outputs for Viewer vs Tests variants

[RyeMutt]

I'm not sure copilot is correct about causing the downstream jobs to fail. The build job only outputs artifacts when running the Viewer variant and I've been using an extremely similar build.yaml in alchemy for nearly a year.