docs: Reset figure DPI before each example (#1096)

I followed the [sphinx-gallery
docs](https://sphinx-gallery.github.io/stable/advanced.html#resetting-before-each-example).

I tried to place `reset_mpl` in a different module in the hopes of
removing the warning about sphinx not being able to cache
`sphinx_gallery_conf`, but I couldn't manage to make the import work. I
noticed sklearn declares a function in `conf.py` as well so I don't
think it's too big a deal.

Closes #675

examples/getting_started/plot_skore_product_tour.py

@@ -131,7 +131,7 @@
 # %%
 import matplotlib.pyplot as plt
 
-fig = plt.figure(layout="constrained", dpi=200)
+fig = plt.figure(layout="constrained")
 plt.plot(df["param_alpha"], df["rmse"])
 plt.xscale("log")
 plt.xlabel("Alpha hyperparameter")

examples/getting_started/plot_working_with_projects.py

@@ -231,7 +231,7 @@ def my_func(x):
 
 x = np.linspace(0, 2, 100)
 
-fig, ax = plt.subplots(layout="constrained", dpi=200)
+fig, ax = plt.subplots(layout="constrained")
 ax.plot(x, x, label="linear")
 ax.plot(x, x**2, label="quadratic")
 ax.plot(x, x**3, label="cubic")

sphinx/conf.py

@@ -64,6 +64,14 @@
     "../examples/model_evaluation/plot_cross_validate",
 ]
 
+
+# https://sphinx-gallery.github.io/stable/advanced.html#resetting-before-each-example
+def reset_mpl(gallery_conf, fname):
+    import matplotlib
+
+    matplotlib.rcParams["figure.dpi"] = 200
+
+
 # sphinx_gallery options
 sphinx_gallery_conf = {
     "examples_dirs": "../examples",  # path to example scripts
@@ -79,6 +87,7 @@
     "backreferences_dir": "generated",
     "doc_module": "skore",
     "default_thumb_file": "./_static/images/[email protected]",
+    "reset_modules": (reset_mpl, "seaborn"),
 }
 
 # intersphinx configuration