`show` ignores `figsize` when plotting multiple images

Describe the bug
When passing a list of images to py4DSTEM.show, the figsize argument is ignored.

To Reproduce

import py4DSTEM
import numpy as np

arr = np.random.rand(128,128)

py4DSTEM.show(arr, figsize=(2,2)) # <-- works
# py4DSTEM.show(arr, figsize=(2, np.nan)) # <-- raises error (as expected)

py4DSTEM.show([arr,arr], figsize=(2,2)) # <-- figsize is not changed
py4DSTEM.show([arr,arr], figsize=(2,np.nan)) # <-- does not raise an error

Expected behavior
figsize should control the size of the figure.

Additional context
For grid plots, the undocumented keyword argument axsize controls the size of each axis in the figure. At a minimum this should be documented, and ideally there should also be a way to get the overall size of the figure.

Start at the py4DSTEM.show entry point and reproduce the single-image and multiple-image examples from the issue, comparing how figsize and axsize are handled. Done means figsize controls the overall figure for image lists, invalid values such as (2, np.nan) are rejected consistently, and the supported grid-sizing behavior is documented.