`optype.numpy.To{}ND` false negatives in mypy

[jorenham]

@pavyamsiri discovered in scipy/scipy-stubs#195 (comment) a false negative in mypy with recursive sequences. This causes e.g. onp.ToFloatND = "huh" to be accepted by mypy.

I raised this in python/mypy#18184.

In the meantime we'll need a workaround, as this directly affects a very large portion of the annotations in scipy-stubs.

[jorenham]

import numpy._typing as _npt
import optype.numpy as onp

def f_np(x: _npt._ArrayLikeFloat_co) -> None: ...
def f_onp(x: onp.ToFloatND) -> None: ...

f_np("duck")  # OK: rejected
f_onp("duck")  # FAIL: accepted (mypy only; pyright rejects)