Experimental: NumPy Interoperability

[woodtp]

This PR introduces C-extensions that handle NumPy interop with Bunch and Grid3D.

New for Bunch:

import numpy as np
from orbit.core.bunch import Bunch

# construct a new Bunch instance from an existing numpy array
coords = np.random.normal(size=(1000, 6))

bunch = Bunch.from_numpy(coords)

# Get the coordinates stored within a bunch
coords = bunch.to_numpy()

# Update coordinates of an existing Bunch instance with the values from an array
bunch.update_from_numpy(coords)

Similarly for Grid3D:

import numpy as np
from orbit.core.spacecharge import Grid3D

nx = ny = nz = 100

np_grid = np.random.normal(size=(nx, ny, nz))


# Initialize grid
g = Grid3D(nx, ny, nz)

# Populate grid with external data
g.from_numpy(np_grid)

# Maybe there should be something like:
# g = Grid3D.from_numpy(np_grid)

# Extract grid data to numpy
np_grid = g.to_numpy()

To test the build:

meson setup build -DPyORBIT_EXPERIMENTAL_WITH_NUMPY=true                                                                                                                                          
meson compile -C ./build
pip install . --config-settings=builddir=./build

Resolves #36