Allow dolfinx.fem.Constant to take native float as value type

[finsberg]

Currently mypy complains on the following code

from mpi4py import MPI
import dolfinx
import numpy as np


mesh = dolfinx.mesh.create_unit_square(MPI.COMM_WORLD, 2, 2)
x = dolfinx.fem.Constant(mesh, 1.0)

with the error

error: Argument 2 to "Constant" has incompatible type "float"; expected "ndarray[Any, Any] | Sequence[Any] | floating[Any] | complexfloating[Any, Any]"  [arg-type]

while the following works

from mpi4py import MPI
import dolfinx
import numpy as np


mesh = dolfinx.mesh.create_unit_square(MPI.COMM_WORLD, 2, 2)
x = dolfinx.fem.Constant(mesh, np.float64(1.0))

In my opinion it is quite annoying to have to wrap all floats in a numpy float, so here I am suggesting to add (native) float as a valid type to dolfinx.fem.Constant

As a side note, the main issue here is really that

import numpy as np

x: np.floating = 1.0

fails in mypy.