no longer ignore errors in method union of DisjointSet

[dcoudert]

Fixes #38939.

This PR changes the declaration of method union from noexcept to except * to properly raise errors.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• 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.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit e93a360; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[tscrim]

LGTM

[gmou3]

Can you please report the time it takes to run

%time matroids.CompleteGraphic(8).circuits()

before and after the change?

[dcoudert]

The slowdown seems rather limited.

Before:

sage: %timeit matroids.CompleteGraphic(3).circuits()
53.3 µs ± 68.4 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
sage: %timeit matroids.CompleteGraphic(4).circuits()
118 µs ± 526 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
sage: %timeit matroids.CompleteGraphic(5).circuits()
1.23 ms ± 9.29 µs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)
sage: %timeit matroids.CompleteGraphic(6).circuits()
23.2 ms ± 92.2 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)
sage: %timeit matroids.CompleteGraphic(7).circuits()
525 ms ± 3.07 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
sage: %timeit matroids.CompleteGraphic(8).circuits()
13.6 s ± 59.2 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

With this PR:

sage: %timeit matroids.CompleteGraphic(3).circuits()
56.6 µs ± 111 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
sage: %timeit matroids.CompleteGraphic(4).circuits()
124 µs ± 756 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)
sage: %timeit matroids.CompleteGraphic(5).circuits()
1.29 ms ± 24.1 µs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)
sage: %timeit matroids.CompleteGraphic(6).circuits()
23.4 ms ± 186 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)
sage: %timeit matroids.CompleteGraphic(7).circuits()
543 ms ± 12.4 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
sage: %timeit matroids.CompleteGraphic(8).circuits()
13.9 s ± 59.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

[gmou3]

Thanks for running the tests.

I suppose the slowdown can be ignored if the error handling is deemed to be of some value.