Allow vmin_vmax to be a callable

[ianhi]

Problem

You can specify vmin_vmax as a slider, and you can individual specify vmin and vmax as functions. But you cannot specify both vmin and vmax using a single function. It would be nice to be able to do something like this (percentile based thresholding)

def vmin_vmax(prange):
    return np.percentile(img, prange)

and then do iplt.imshow(img, prange(1,99,99), vmin_vmax=vmin_vmax)

Proposed Solution

Add yet more special casing to vmin_vmaxto allow this.

I think a check if it's a callable goes here: https://github.com/ianhi/mpl-interactions/blob/94cfc2a9d9f3be9091c47bf329ed2e309edbab94/mpl_interactions/controller.py#L110-L112

(and in mpl equivalent) and similarly here:
https://github.com/ianhi/mpl-interactions/blob/94cfc2a9d9f3be9091c47bf329ed2e309edbab94/mpl_interactions/controller.py#L154-L156

This will also require keeping tracking of which params the function accepts and should maintain the ability to access controls.params['vmin_vmax']

Additional context

[ianhi]

I think I may have backed myself into a corner here where each controls object can only have a single vmin_vmax. This is because I really want to be able to do ctrls['vmin']

If vmin_vmax is a function then it should be possible to pass different functions to each iplt call.

def vmin_vmax1(...):

def vmin_vmax2(...):

ctrls = iplt.imshow(..., vmin_vmax = vmin_vmax1, ax = axs[0])
iplt.imshow(..., vmin_vmax = vmin_vmax2, ax = axs[1], controls=ctrls)

but if we allow that then there is no easy way to define ctrls['vmin']. I think this is an issue because this is the only dynamically defined kwarg that we have.

[ianhi]

Maybe the solution is to create a transformed kwarg object?

from mpl_interactions import transformed_kwarg, Controls

def vmin_vmax(prange):
    # do something complicated
    return (vmin, vmax)
vv_kwarg = transformed_kwarg('prange', vmin_vmax),  # just use signature inspect here?
# or maybe have `kwargs=None` which defaults to using signature inspect

Controls(prange= ('r', 1, 99, 99), vmin_vmax = vv_kwarg) # vmin = transformed_kwarg....

where the vmin = is a default transformation that magically does the right thing