gh-35186: Various improvements to Weyl character rings
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### 📚 Description
We provide a number of improvements to the Weyl character ring:
1. We make it know that it is commutative (along with its ambient ring).
2. We speedup the `_demazure_helper` method by only doing operations
based upon the support of the simple roots.
```
sage: F = FusionRing(['B',10], 2, base_ring=QQ)
sage: dd = {(1,0,0,1,0,0,0,0,0,0): 1}
sage: %time X = F._demazure_helper(dd)
CPU times: user 3.1 s, sys: 12 ms, total: 3.11 s
Wall time: 3.11 s
```
Previously took `~6s`.
3. We don't set the `FusionRing` as a subobject of the `WeightRing`.
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URL: https://github.com/sagemath/sage/pull/35186
Reported by: Travis Scrimshaw
Reviewer(s): Dima Pasechnik
