ENH: add reusable matplotlib stylesheet

[neutrinoceros]

PR Summary

Adresses #4342, but doesn't close it because I'm holding off on automated testing until we get pytest_mpl started.

Here are my manual tests for it

import matplotlib as mpl
import matplotlib.pyplot as plt
import yt

from packaging.version import Version
from yt.visualization._commons import MPL_VERSION

print(f'{MPL_VERSION=}')


with yt.funcs.matplotlib_style_context():
    fig, ax = plt.subplots()
    ax.plot([0, 1], [0, 1])
    ax.set(xlabel=r"$\Sigma$", ylabel=r"$\beta$", title="My fake yt plot")
    fig.savefig("/tmp/yt_style_funcs.png")

if MPL_VERSION >= Version("3.7"):
    with plt.style.context("yt.default"):
        fig, ax = plt.subplots()
        ax.plot([0, 1], [0, 1])
        ax.set(xlabel=r"$\Sigma$", ylabel=r"$\beta$", title="My fake yt plot")
        fig.savefig("/tmp/yt_style_plt_context.png")

    with mpl.style.context("yt.default"):
        fig, ax = plt.subplots()
        ax.plot([0, 1], [0, 1])
        ax.set(xlabel=r"$\Sigma$", ylabel=r"$\beta$", title="My fake yt plot")
        fig.savefig("/tmp/yt_style_mpl_context.png")

    mpl.style.use("yt.default")
    fig, ax = plt.subplots()
    ax.plot([0, 1], [0, 1])
    ax.set(xlabel=r"$\Sigma$", ylabel=r"$\beta$", title="My fake yt plot")
    fig.savefig("/tmp/yt_style_mpl_use.png")

I still plan on adding a minimal test with no actual image comparison, just to make sure this works with minimal requirements too (which i have checked manually).
I will also need to add documentation.

PR Checklist

• New features are documented, with docstrings and narrative docs
• [N/A] Adds a test for any bugs fixed. Adds tests for new features.
• make sure the new file is correctly bundled in builds

[neutrinoceros]

I may have missed the point of matplotlib_style_context's default behaviour. I assumed it was meant to reproduce yt's style, when it may be a simple backport of matplotlib.style.context for older versions of matplotlib (in which case it's not needed now).
I will focus on getting CI green for now, and I'll come back to this part.

update (answering my own concerns): There may have been a couple competing ideas in the original design of the function, but I'm going to go with my original assumption that it's meant to reproduce yt's style, to some extent, because it is used internally without any arguments.

[neutrinoceros]

Actually, turns out this is already minimally tested since matplotlib_style_context is used internally.

[neutrinoceros]

hint to reviewers: this option is the reason why I'm dropping support for matplotlib 3.2 in the same PR (it's invalid before matplotlib 3.3). Previously this was handled dynamically but this behaviour cannot be replicated with a static style sheet.

[neutrinoceros]

For reference here's the current output of the example I'm giving in the docs:

Does it feels like yt enough ? Am I missing some of the parameters that make up for yt's style ?

[matthewturk]

I do like this idea! Will go over in detail.

[matthewturk]

Sorry for letting this languish! I think it's good to go in, don't you?

[neutrinoceros]

I think I should revisit this to avoid data duplication in yt.visualization._commons.DEFAULT_FONT_PROPERTIES, and simplify how it's constructed by using matplotlib API if possible. Switching to draft for now

[neutrinoceros]

Turns out the nice API I was hoping for doesn't exist (yet ?) so I'll just push one more time to fix type-checking, and now I believe it's ready to go @matthewturk

[neutrinoceros]

Well looking back, I actually ended up removing the one parameter that justified dropping support for MPL 3.2, so I'll revert this now.