gh-37787: modernize coercion for Hecke algebras
Small changes that switch Hecke algebras to the modern coercion
framework.
<s>Also avoiding the auld class `CommutativeRing` and use the categories
instead.</s>
### :memo: Checklist
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [x] I have updated the documentation accordingly.
URL: https://github.com/sagemath/sage/pull/37787
Reported by: Frédéric Chapoton
Reviewer(s): Travis Scrimshaw
