Test and bugfix equality testing with different degree polynomials.

### What is wrong?

If I read the current implementation of `FQP.__eq__` correctly, it returns `True` for this test:

```py
FQP([1, 2, 3], ...) == FQP([1, 2], ...)
```
which seems wrong.

In the current implementation, `zip` terminates on the shorter list, and there's no explicit length/degree check.

### How can it be fixed

Add tests for related scenarios, and make sure implementation is correct.

Also, because of the type checking involved, make sure that the equality test is commutative when the class is different, like:
```py
fq2_a = FQP([2, 3], (1, 0))
fq2_b = FQ2([2, 3], (1, 0))

assert fq2_a == fq2_b
assert fq2_b == fq2_a