gh-38655: trying to refresh symbolic units
by allowing the conversion constants in the stored data to be either
strings or rationals
Part of the conversion table are replaced by integers or rational but
not systematically.
This file is not correctly indented, but this is not fixed here.
### :memo: Checklist
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- [x] The title is concise and informative.
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- [ ] 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.
URL: https://github.com/sagemath/sage/pull/38655
Reported by: Frédéric Chapoton
Reviewer(s): Travis Scrimshaw
