Using with `matplotlib.testing.decorators.image_comparison`

Nobody has claimed this yet.

The problem is that the baseline images generated locally (in a Dev Container) don't match the ones on CI (GitHub Actions running the latest Ubuntu LTS) and thus my tests fail. When I compared the images I figured out that different fonts are being used: CI's Ubuntu has more fonts pre-installed than a Dev Container so the text was rendered with `Liberation Sans` instead of `DejaVu Sans`.

To quick fix it:

1. Install Liberation fonts locally
`sudo apt install fonts-liberation`
2. Drop `matplotlib` fonts cache (file location and name can be different)
`rm ~/.cache/matplotlib/fontlist-v330.json`
4. Re-generate baseline images

Also to find a solution that won't fail when some font is added/removed locally/remotely, I dug deeper and figured out that `matpltolib` has a solution for this well-known issue: [matplotlib.testing.setup()](https://github.com/matplotlib/matplotlib/blob/v3.8.3/lib/matplotlib/testing/__init__.py#L28) that calls [set_font_settings_for_testing()](https://github.com/matplotlib/matplotlib/blob/v3.8.3/lib/matplotlib/testing/__init__.py#L18) that sets `font.family` to `DejaVu Sans`.

But for `mplfinance` that makes no difference because the `font.family` gets overridden by [_apply_mpfstyle](https://github.com/matplotlib/mplfinance/blob/e0eaa075ca4dfb81246c4074d58380fdb1f3c9a8/src/mplfinance/_styles.py#L19) call. For example, the `default` style sets it to `sans-serif` (comes from `base_mpl_style='seaborn-darkgrid'`), and then nobody knows which font `maptlotlib` is going to use for rendering.

Here I came up with two solutions:

### `pytest` fixture

Pros:
- uses only public API

Cons:
- need to pass to every `.plot(...)`

```py
@pytest.fixture
def mpf_style():
return mpf.make_mpf_style(
base_mpf_style="default", rc={"font.family": "DejaVu Sans"}
)

@image_comparison(baseline_images=["test.png"])
def test(mpf_style):
mpf.plot(..., style=mpf_style)
```

### `pytest` before-all hook that mutates `default` style

Pros:
- all the existing tests left untouched
- never forget passing `style=...` in new ones

Cons:
- gets broken on the underlying `mplfinance` implementation changes

```py
def pytest_configure() -> None:
mpf._styledata.default.style["rc"].append(("font.family", "DejaVu Sans"))
```

Start by reading src/mplfinance/_styles.py, especially _apply_mpfstyle, and compare it with matplotlib.testing.setup() and set_font_settings_for_testing(). Review the image-comparison tests and determine which approach keeps rendered fonts consistent between local Dev Containers and GitHub Actions without requiring each test to pass a custom style; done means the existing baseline comparisons pass in both environments.

Written by the indexing model from the issue text.