llvmlite 0.42.0rc1 Checklist

llvmlite 0.42.0

[x] Merge to main.
- nothing new
[x] Create 0.42 release branch release0.42
- [ ] Update CHANGE_LOG in a PR targeting the release branch.
- [ ] Follow the format of previous CHANGE_LOG entries.
[x] Get the change-log-PR reviewed and merged.
[x] Test HEAD of release branch on buildfarm (pre-tag testing):
- [x] conda package build and test. llvmlite_269
- [x] wheel build. llvmlite_wheel_57
[x] Annotated tag v0.42.0rc1 on release branch (llvmlite tags DO have a v prefix).
[x] Build and upload conda packages on buildfarm (check "upload"). llvmlite_270
[x] Build wheels and sdist on the buildfarm (check "upload"). llvmlite_wheel_58
[x] Verify packages uploaded to Anaconda Cloud and copy to numba/label/main.
[x] Upload wheels and sdist to PyPI. (upload from ci_artifacts).
[x] Verify wheels for all platforms arrived on PyPi.
[x] Initialize and verify ReadTheDocs build.
[x] Send RC announcement email / post announcement to discourse group.
[ ] Post link to X and Mastodon and anywhere else that is appropriate.

[x] Clean up ci_artifacts by moving files to subdirectories
[x] Tag 0.43.0dev0 to start new development cycle on main.
[x] Update release checklist template with any additional bullet points that may have arisen during the release.
[x] Close milestone (and then close this release issue).