Add a bit more logging

Add a bit more logging

Use named capture groups for version string matching

Previously it was referencing the wrong group index (off by one), which is easy to do when relying on indices. Using capture groups here should make it less error prone (and also fixes this initial problem).

Long term a small unit test should avoid this happening / regressing.

github: add separate README

This README will show up in the repo root on GitHub only. It explains
that the repository is mirrored and directs users to the canonical
Codeberg repository.

Handle `zig env` being ZON instead of JSON

main: fix canonical URL

Use ziglang.org community mirrors list

This new list supersedes the `mirrors.json` in this repo.

npm update

Notably, this gets us `@actions/github` 6.0.1, which is necessary for
`github.context.runAttempt` (so I have also updated `package.json`
accordingly). On that note... great job following semver, GitHub!
Between this and the non-breaking major version change on
`@actions/cache`, I'm starting to feel like nobody on the Actions team
understands how software versioning works.

fix: handle new tarball name format as of 0.14.1

README: reference setup-zig@v2