use pkg-config to find msolve, otherwise try to run it

[dimpase]

spkg-config.m4 for msolve

This will fix #38315

So far, it's not possible to find msolve's version by running it, but it should be fixed in the future by algebraic-solving/msolve#147

📝 Checklist

• [ x] The title is concise and informative.
• [ x] The description explains in detail what this PR is about.
• [ x] I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

[github-actions]

Documentation preview for this PR (built with commit 5c875f4; changes) is ready! 🎉
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[dimpase]

there are no dependencies checks in spkg-configure.m4, as we only use an executable which is already self-sufficient.
(it would have to change if we had an library interface to msolve)

[mezzarobba]

Thank you! Lgtm.

[dimpase]

a trivial rebase, back to positive review