gh-37415: make EllipticCurvePoint_field inherit from EllipticCurvePoint
The method `EllipticCurve_generic.__contains__()` checks for inheritance
from `EllipticCurvePoint`; however, the other classes for points on
elliptic curves do not inherit from this class. This pull request fixes
this. Note that there is some overlap with #33228.
This change makes `P in E` much faster:
- Over **Q**:
```python
E = EllipticCurve('37a1')
P = E((0, -1))
%timeit P in E
```
Before: `35.3 µs ± 186 ns per loop (mean ± std. dev. of 7 runs, 10,000
loops each)`
After: `324 ns ± 0.535 ns per loop (mean ± std. dev. of 7 runs,
1,000,000 loops each)`
- Over a finite field:
```python
F.<a> = FiniteField((23, 2), modulus='random')
E = EllipticCurve_from_j(F.random_element())
P = E.random_point()
%timeit P in E
```
Before: `36.4 µs ± 542 ns per loop (mean ± std. dev. of 7 runs, 10,000
loops each)`
After: `333 ns ± 5.03 ns per loop (mean ± std. dev. of 7 runs, 1,000,000
loops each)`
URL: https://github.com/sagemath/sage/pull/37415
Reported by: Peter Bruin
Reviewer(s): Kwankyu Lee, Peter Bruin
