Use link check from the CLI instead of an action

[rogermparent]

This PR changes our usage of our repo-link-check package in GitHub Actions to use its CLI interface instead of the checks-action-based reporting. The latter has always caused us a bunch of issues, one we always encounter being an issue with passing data around in PRs with huge diffs like #3396.

The output will be a little less friendly looking, but a slight trade-off in readability is worth the reliability IMO.

[rogermparent]

I didn't realize the large diff issue wasn't due to GitHub Actions, but child_process.exec's buffer limitations. I can think of a few fixes to that, all involving a small upgrade to the link check package itself. I still think this is the way to go, but I'll shelve it for now until we add link-check to mlem.ai and get the VSCode extension released.

[rogermparent]

Superceded by #3700