MUSL support

[cretz]

What was changed

• Updated (and tested) the build-gems.yml CI workflow to build musl gems
  • Did not do in Alpine-based regular CI (requires lots of changes because setup-ruby and other things don't work there, and we have smoke test anyways)
  • Updated smoke test to run in Alpine container
  • Due to Ruby google-protobuf linux precompiled gem crash with Segmentation fault on linux-musl protocolbuffers/protobuf#16853, had to use "ruby" platform Google Protobuf gem in smoke test (builds manually on install)
• Updated README

Checklist

1. Closes [Feature Request] Build musl gem #215

[mjameswh]

That's saying you will no longer run this for Ruby 3.3 on non-musl. Is this really what you meant?

[cretz]

This actually adds a new single entry to the matrix due to the field below this one for setting a container different than an existing metric. It does not affect existing ones. See https://github.com/temporalio/sdk-ruby/actions/runs/13185031590. In fact, since we install Ruby a different way for Alpine, technically I could set this to any value because it is not used for this specific matrix entry.

[mjameswh]

due to the field below this one for setting a container different than an existing metric

Oh, right… very subtle. I'd suggest a comment.