refactor(plot): return plotting objects instead of storing attributes

[Sharkyii]

This PR refactors all Display.plot() methods to return the plotting object instead of storing them as attributes on the display instance.

Previously, calling .plot() created attributes such as figure_, ax_,. These attributes did not exist before plotting, which introduced hidden state and allowed external mutation of internal display objects.

Fixes #2374

Follow up -
Edit other test file to work with the new pattern

[Sharkyii]

@auguste-probabl could you review this PR?
If the direction looks good, I’ll continue updating the remaining tests.

[auguste-probabl]

If the direction looks good, I’ll continue updating the remaining tests.

Yep, I think this works fine, thanks!

[Sharkyii]

@auguste-probabl could you please review this when you have a moment? I’ll double-check again in the meantime to ensure all tests are passing.

[github-actions]

Documentation preview @ 7909769

[github-actions]

Coverage Report for skore/

File	Stmts	Miss	Cover	Missing
skore/src/skore
__init__.py	26	0	100%
_config.py	31	0	100%
_login.py	14	0	100%
exceptions.py	4	4	0%	4, 15, 19, 23
skore/src/skore/_sklearn
__init__.py	6	0	100%
_base.py	73	8	89%	272–279
feature_names.py	26	0	100%
find_ml_task.py	61	0	100%
types.py	28	1	96%	30
skore/src/skore/_sklearn/_comparison
__init__.py	7	0	100%
inspection_accessor.py	27	1	96%	124
metrics_accessor.py	166	2	98%	179, 1138
report.py	111	3	97%	488, 491, 497
utils.py	57	0	100%
skore/src/skore/_sklearn/_cross_validation
__init__.py	9	0	100%
data_accessor.py	40	0	100%
inspection_accessor.py	20	1	95%	116
metrics_accessor.py	169	5	97%	1054, 1115, 1118, 1144–1145
report.py	126	3	97%	498, 501, 507
skore/src/skore/_sklearn/_estimator
__init__.py	9	0	100%
data_accessor.py	63	2	96%	86, 190
inspection_accessor.py	70	2	97%	315, 329
metrics_accessor.py	367	6	98%	427, 431, 446, 476, 1661, 1744
report.py	158	2	98%	463, 466
skore/src/skore/_sklearn/_plot
__init__.py	3	0	100%
base.py	57	2	96%	59–60
utils.py	121	2	98%	273–274
skore/src/skore/_sklearn/_plot/data
__init__.py	2	0	100%
table_report.py	178	1	99%	669
skore/src/skore/_sklearn/_plot/inspection
__init__.py	0	0	100%
coefficients.py	210	0	100%
impurity_decrease.py	62	1	98%	175
permutation_importance.py	152	0	100%
utils.py	9	0	100%
skore/src/skore/_sklearn/_plot/metrics
__init__.py	6	0	100%
confusion_matrix.py	157	0	100%
metrics_summary_display.py	8	0	100%
precision_recall_curve.py	109	0	100%
prediction_error.py	152	0	100%
roc_curve.py	113	0	100%
skore/src/skore/_sklearn/train_test_split
__init__.py	0	0	100%
train_test_split.py	58	0	100%
skore/src/skore/_sklearn/train_test_split/warning
__init__.py	8	0	100%
high_class_imbalance_too_few_examples_warning.py	19	1	94%	83
high_class_imbalance_warning.py	20	0	100%
random_state_unset_warning.py	10	0	100%
shuffle_true_warning.py	9	0	100%
stratify_is_set_warning.py	10	0	100%
time_based_column_warning.py	21	0	100%
train_test_split_warning.py	3	0	100%
skore/src/skore/_utils
__init__.py	6	2	66%	8, 13
_accessor.py	112	3	97%	38, 214, 268
_cache.py	37	0	100%
_environment.py	32	2	93%	41, 44
_fixes.py	8	0	100%
_index.py	5	0	100%
_logger.py	22	4	81%	15–17, 19
_measure_time.py	10	0	100%
_parallel.py	38	3	92%	23, 33, 124
_patch.py	21	12	42%	30, 35–39, 42–43, 46–47, 58, 60
_progress_bar.py	41	4	90%	55–56, 66–67
_show_versions.py	38	0	100%
_testing.py	103	11	89%	20, 29, 157, 166, 177–182, 184
skore/src/skore/_utils/repr
__init__.py	2	0	100%
base.py	54	0	100%
data.py	163	0	100%
html_repr.py	38	0	100%
rich_repr.py	81	0	100%
skore/src/skore/project
__init__.py	2	0	100%
_summary.py	75	1	98%	119
_widget.py	187	0	100%
project.py	55	0	100%
TOTAL	4295	89	97%

Tests	Skipped	Failures	Errors	Time
1649	5 💤	0 ❌	0 🔥	6m 8s ⏱️

[Sharkyii]

@auguste-probabl All tests are passing on my side - ready for review.