gh-37375: Speed up square matrix times vector over GF(2)
When doing a matrix-times-vector multiplication over F_2, there is some
inefficiency caused by calling `VectorSpace` to create a parent for the
result. This becomes noticeable when repeatedly multiplying small
matrices.
When the dimensions are all the same, this can be improved by using the
parent of the vector also as the parent for the result. Before:
```
sage: A = random_matrix(GF(2),10,10)
sage: v0 = vector(random_matrix(GF(2),10,1))
sage: %timeit A*v0
2.26 µs ± 4.57 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops
each)
```
After:
```
sage: A = random_matrix(GF(2),10,10)
sage: v0 = vector(random_matrix(GF(2),10,1))
sage: %timeit A*v0
981 ns ± 9.57 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops
each)
```
URL: https://github.com/sagemath/sage/pull/37375
Reported by: kedlaya
Reviewer(s): Lorenz Panny
