Removing use of deprecated alias of VersionChange

[rptb1]

Deprecated alias sphinx.directives.other.VersionChange was removed in Sphinx 8 https://www.sphinx-doc.org/en/master/changes/8.0.html#release-8-0-0-released-jul-29-2024 and this breaks the manual build.

This also breaks manual builds on Read The Docs, e.g. https://readthedocs.org/projects/memory-pool-system/builds/26405165/

Update to the recommended sphinx.domains.changeset.VersionChange.

[rptb1]

Executing proc.review.express.

1. Start time 11:39.
2. Applying entry.universal. Source documents are linked above. Applying entry.impl. Read The Docs build succeeded and output is visible.
3. Calling in @thejayps . There will be a short delay.

[rptb1]

Executing proc.review.check.

1. Start time 12:55.
2. Checked out the branch and ensured I could build the manual with:

cd manual
make clean
rm -r tool
make html

3. Checked the Sphinx version of the successful manual build with ./tool/bin/sphinx-build --version and got "sphinx-build 8.1.3" which matches the version run by Read the Docs.
4. Checking finished 12:59.

[thejayps]

Checking - no defects found after 6 minutes

[rptb1]

Continuing proc.review.express.
4. proc.review.express.brainstorm: This is another software rot defect that would be caught earlier by fixing #294 . Was there a deprecation warning from Sphinx that we missed?
5. proc.review.exit.pass: Change passed.
6. proc.review.exit.calc: About 40 minutes used.

[thejayps]

@rptb1 has done exit.pass

[rptb1]

Executing proc.merge.pull-request.

1. Start time 13:12.
2. Using the GitHub merge button instead of section 5, "Merging procedure" because this is a one-commit change with low risk and I already built the branch during checking.
3. End time 13:14.