gh-36571: Add method to check whether a (di)graph is geodetic
A (di)graph is geodetic if there exists only one shortest path between
any pair of its vertices. We add a method to check this property on
unweighted (di)graphs.
### :memo: Checklist
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- [x] The description explains in detail what this PR is about.
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- [x] I have created tests covering the changes.
- [x] I have updated the documentation accordingly.
### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/36571
Reported by: David Coudert
Reviewer(s): David Coudert, Kwankyu Lee
