fix(skore-local-project): Clear the report cache instead of deleting it before serialization

[thomass-dev]

The attribute _cache can't be missing after depickling the report:

File skore/_sklearn/_estimator/metrics_accessor.py:1461, in _MetricsAccessor._rmse(self, data_source, data_source_hash, X, y, multioutput)
   1439 @available_if(
   1440     _check_supported_ml_task(
   1441         supported_ml_tasks=["regression", "multioutput-regression"]
   (...)   1453     ) = "raw_values",
   1454 ) -> float | list:
   1455     """Private interface of `rmse` to be able to pass `data_source_hash`.
   1456 
   1457     `data_source_hash` is either an `int` when we already computed the hash
   1458     and are able to pass it around or `None` and thus trigger its computation
   1459     in the underlying process.
   1460     """
-> 1461     result = self._compute_metric_scores(
   1462         metrics.root_mean_squared_error,
   1463         X=X,
   1464         y_true=y,
   1465         data_source=data_source,
   1466         data_source_hash=data_source_hash,
   1467         response_method="predict",
   1468         multioutput=multioutput,
   1469     )
   1470     if (
   1471         self._parent._ml_task == "multioutput-regression"
   1472         and multioutput == "raw_values"
   1473     ):
   1474         return cast(list, result)

File skore/_sklearn/_estimator/metrics_accessor.py:475, in _MetricsAccessor._compute_metric_scores(self, metric_fn, X, y_true, response_method, data_source, data_source_hash, pos_label, **metric_kwargs)
    471         cache_key_parts.append(value)
    473 cache_key = tuple(cache_key_parts)
--> 475 if cache_key in self._parent._cache:
    476     score = self._parent._cache[cache_key]
    477 else:

AttributeError: 'EstimatorReport' object has no attribute '_cache'

[github-actions]

Coverage Report for skore-local-project/

File	Stmts	Miss	Cover	Missing
skore-local-project/src/skore_local_project
__init__.py	5	0	100%
metadata.py	88	4	95%	22, 32, 149–150
project.py	102	1	99%	250
storage.py	40	2	95%	45, 187
TOTAL	235	7	97%

Tests	Skipped	Failures	Errors	Time
23	0 💤	0 ❌	0 🔥	6.518s ⏱️