Replace custom `nan_to_num` with Numba's implementation

[Saransh-cpp]

Vector has a custom Numba implementation of numpy.nan_to_num -

vector/src/vector/backends/_numba_object.py

Lines 54 to 55 in 6ba5a60

	@numba.extending.overload(numpy.nan_to_num) # FIXME: This needs to go into Numba!
	def nan_to_num(x, copy=True, nan=0.0, posinf=None, neginf=None):

which should ideally by in Numba.

The feature request was raised by Jim in numba/numba#6857 and the function was partially implemented in numba/numba#8623. I have opened a new issue for a complete implementation - numba/numba#10089 - and we should be ready to remove our custom implementation once this issue is closed.

[Saransh-cpp]

Blocked by #641