Show release notes for all versions of MUSE2 in old versions of docs

[alexdewar]

Description

When you navigate to an old version of the docs (since v2.1.0), there will be chapters for release notes for all the different versions of MUSE2 listed in the navigation bar, but it will only show the release notes that were bundled in the old version of the docs, i.e. no newer versions. For v2.0.0, there are no release notes included in the docs anyway, which is less of a problem, but only showing release notes for some versions of MUSE2 is potentially confusing. This isn't a problem now, but once we've released v2.2.0, the release notes for this won't appear in the docs for v2.1.0 etc., so we should fix it.

I've changed the build_old_docs.py script to substitute in the release notes from the dev version of the docs, so they should always be up to date. It does this by patching SUMMARY.md (which has the TOC) and symlinking/copying the docs/release_notes folder. I had to add a couple of patch files to the old versions of the docs to make this work, but we shouldn't need to do this going forward.

As part of this, I changed the way the git repo is used. Previously, we cloned the whole thing to a temp dir, then checked out the different versions one by one. Now that we're mucking about with the git tree by deleting files etc., it makes it messier to change between the different tags, so I switched to using a different worktree for each instead.

While I was at it, I fixed #1189.

Closes #1251. Closes #1189.

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc
• Update release notes for the latest release if this PR adds a new feature or fixes a bug
  present in the previous release

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.76%. Comparing base (1aa603d) to head (5a8208f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1268   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files          57       57           
  Lines        8210     8210           
  Branches     8210     8210           
=======================================
  Hits         7370     7370           
  Misses        544      544           
  Partials      296      296           

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[Copilot]

Pull request overview

Updates the “old docs” build pipeline so older documentation versions always include the latest MUSE2 release notes (avoiding confusing partial release-note navigation in historical docs), and makes the old-docs build process safer to modify by switching from checkout-in-place to per-release git worktrees.

Changes:

• Add “release notes” anchor markers in docs/SUMMARY.md (and via patches in v2.0.0/v2.1.0) so the old-docs builder can replace the release-notes section consistently.
• Update docs/build_old_docs.py to (a) build each release from its own git worktree, and (b) inject the current release-notes TOC + link/sync docs/release_notes into each old-docs build.
• Add a v2.0.0 patch to include the “Other versions of documentation” placeholder chapter (fixes #1189).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docs/build_old_docs.py	Switches old-doc builds to worktrees and patches old SUMMARY.md + release_notes directory to always use latest release notes.
docs/SUMMARY.md	Adds anchor comments delimiting the release-notes section for extraction/substitution.
docs/release/patches/v2.1.0/0001-SUMMARY.md-Add-release-notes-anchors.patch	Adds release-notes anchors to v2.1.0 docs so the builder can replace that section.
docs/release/patches/v2.0.0/0002-Add-placeholder-other-versions-of-docs-chapter.patch	Adds “Other versions of documentation” entry to v2.0.0 SUMMARY.
docs/release/patches/v2.0.0/0003-SUMMARY.md-Add-release-notes-anchors.patch	Adds release-notes anchors to v2.0.0 SUMMARY so the builder can inject current release notes.

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