gh-35643: Avoid redundant computations in finite field .conjugate() method
### :books: Description
The previous implementation was factoring the order
(characteristic^degree) to obtain the field degree.
The methods `cardinality()` and `order()` are really defined as `return
self.characteristic()**self.degree()`.
Sage 10rc3
```
sage: p = next_prime(2**160)
sage: K = GF((p,2))
sage: x = K.random_element()
sage: %timeit x.conjugate()
13.2 ms ± 77.8 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
```
After patch:
```
sage: %timeit x.conjugate()
5.01 µs ± 15.5 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops
each)
```
### :memo: Checklist
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.
### :hourglass: Dependencies
None
URL: https://github.com/sagemath/sage/pull/35643
Reported by: Rémy Oudompheng
Reviewer(s): Lorenz Panny
