Fix continuous integration

Continuous integration has been broken from several years of non-use, and older runners (`ubuntu-20.04`) falling out of existence. CI for this is going to be disabled as a result, until it can be fixed.

This issue is to track re-enabling CI with something more robust and unlikely to break. Now that we have an `alloy-dev-container`, perhaps this should be leveraged for the `clang` and `clang-cl` builds targeting both Linux or Windows -- since we can leverage mingw64 on Linux for cross-compilation. At which point, we can potentially leverage dev-containers

## Acceptance Criteria

1. CI can run for `clang` builds
2. CI can run for `clang-cl` windows builds
3. CI can run for `clang` macOS builds

No specific CI file or test is named. Start by locating the disabled CI configuration and reviewing the alloy-dev-container proposal, then verify that CI runs clang builds plus clang-cl Windows and clang macOS builds as listed in the acceptance criteria.

Written by the indexing model from the issue text.