Update CI setup

[hexaeder]

Modernizes the CI and docs setup.

• CI: workflow_dispatch, cancel superseded runs, fixed JULIA_CPU_TARGET=x86-64-v3 so cached pkgimages load on every runner. Coverage is collected and uploaded only on the release version.
• Docs: the docs project is a workspace member of the package ([workspace] plus [sources]). make.jl deploys the preview even if makedocs hit errors, then fails CI afterwards. DOCUMENTER_DRAFT builds into docs/build_draft.
• Preview cleanup: the per-PR cleanup on close is replaced by a daily scheduled job, which deletes the previews of all closed PRs and squashes the gh-pages history.
• Compat: adds compat entries for the stdlibs and test deps. Plain "1" for the stdlibs resolves and passes the tests on Julia 1.6 and 1.10.

Closes #101, closes #102, closes #103.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.52%. Comparing base (7264d87) to head (599c2a6).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #106      +/-   ##
==========================================
+ Coverage   97.28%   97.52%   +0.24%     
==========================================
  Files          11       11              
  Lines         736      728       -8     
==========================================
- Hits          716      710       -6     
+ Misses         20       18       -2     

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