Improve workaround and also apply it for surrogate model renaming

baybe/recommenders/base.py

@@ -4,6 +4,7 @@
 
 import cattrs
 import pandas as pd
+from cattrs import override
 
 from baybe.objectives.base import Objective
 from baybe.searchspace import SearchSpace
@@ -51,15 +52,35 @@ def recommend(
         ...
 
 
+# TODO: The workarounds below are currently required since the hooks created through
+#   `unstructure_base` and `get_base_structure_hook` do not reuse the hooks of the
+#   actual class, hence we cannot control things there. Fix is already planned and also
+#   needed for other reasons.
+
 # Register (un-)structure hooks
 converter.register_unstructure_hook(
     RecommenderProtocol,
     lambda x: unstructure_base(
         x,
         # TODO: Remove once deprecation got expired:
-        overrides=dict(acquisition_function_cls=cattrs.override(omit=True)),
+        overrides=dict(
+            acquisition_function_cls=cattrs.override(omit=True),
+            # Temporary workaround (see TODO note above)
+            _surrogate_model=override(rename="surrogate_model"),
+            _current_recommender=override(omit=False),
+            _current_recommender_was_used=override(omit=False),
+        ),
     ),
 )
 converter.register_structure_hook(
-    RecommenderProtocol, get_base_structure_hook(RecommenderProtocol)
+    RecommenderProtocol,
+    get_base_structure_hook(
+        RecommenderProtocol,
+        # Temporary workaround (see TODO note above)
+        overrides=dict(
+            _surrogate_model=override(rename="surrogate_model"),
+            _current_recommender=override(omit=False),
+            _current_recommender_was_used=override(omit=False),
+        ),
+    ),
 )

baybe/recommenders/meta/base.py

@@ -20,24 +20,11 @@
 class MetaRecommender(SerialMixin, RecommenderProtocol, ABC):
     """Abstract base class for all meta recommenders."""
 
-    # TODO: The attributes should be `init=False` but this currently prevents them from
-    #   being serialized. The reason is that setting `_cattrs_include_init_false=True`
-    #   for this class has currently no effect when serializing it as
-    #   a `RecommenderProtocol`, since the hook of the latter does not reuse the
-    #   hook of the actual class. Fix is already planned and also needed for other
-    #   reasons. Until that, as a workaround, we expose the attributes as "private"
-    #   attributes.
-
-    _current_recommender: PureRecommender | None = field(
-        alias="_current_recommender", default=None, kw_only=True
-    )
-    """The current recommender. (For internal use only!)"""
-
-    _current_recommender_was_used: bool = field(
-        alias="_current_recommender_was_used", default=False, kw_only=True
-    )
-    """Flag indicating if the current recommender has already been used.
-    (For internal use only!)"""
+    _current_recommender: PureRecommender | None = field(default=None, init=False)
+    """The current recommender."""
+
+    _current_recommender_was_used: bool = field(default=False, init=False)
+    """Flag indicating if the current recommender has already been used."""
 
     @abstractmethod
     def select_recommender(