gh-36095: Implementing a generic one method for unital algebras
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We implement a generic `one()` method for unital algebras in order to
fix the following:
```python
sage: S2 = simplicial_complexes.Sphere(2)
sage: H = S2.cohomology_ring(QQ)
sage: C = cartesian_product([H, H])
sage: C.one() # this raises an error currently
B[(0, (0, 0))] + B[(1, (0, 0))]
```
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URL: https://github.com/sagemath/sage/pull/36095
Reported by: Travis Scrimshaw
Reviewer(s): Frédéric Chapoton
