feat(algebra/field_power): fpow is a strict mono (#1778)
* WIP
* feat(algebra/field): remove is_field_hom
A field homomorphism is just a ring homomorphism.
This is one trivial tiny step in moving over to bundled homs.
* Fix up nolints.txt
* Process comments from reviews
* Rename lemma
![mergify[bot]](https://avatars.githubusercontent.com/in/10562?v=4&s=60)