Move documentation from the module to the class

The module documentation is not being included in the rendered docs.
Normally this is done by including it in the User Guide, but since this
is an experimental module, we don't want to include it yet, so it is
easier to just move the docs to the class so they are rendered in the
API documentation.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/channels/experimental/_grouping_latest_value_cache.py

@@ -1,43 +1,7 @@
 # License: MIT
 # Copyright © 2025 Frequenz Energy-as-a-Service GmbH
 
-"""The GroupingLatestValueCache caches the latest values in a receiver grouped by key.
-
-It provides a way to look up on demand, the latest value in a stream for any key, as
-long as there has been at least one value received for that key.
-
-[GroupingLatestValueCache][frequenz.channels.experimental.GroupingLatestValueCache]
-takes a [Receiver][frequenz.channels.Receiver] and a `key` function as arguments and
-stores the latest value received by that receiver for each key separately.
-
-The `GroupingLatestValueCache` implements the [`Mapping`][collections.abc.Mapping]
-interface, so it can be used like a dictionary. It is not
-a [`MutableMapping`][collections.abc.MutableMapping] because users can't mutate the
-cache directly, it is only mutated by the underlying receiver. There is one exception
-though, users can clear individual keys from the cache using the
-[clear][frequenz.channels.experimental.GroupingLatestValueCache.clear] method.
-
-Example:
-    ```python
-    from frequenz.channels import Broadcast
-    from frequenz.channels.experimental import GroupingLatestValueCache
-
-    channel = Broadcast[tuple[int, str]](name="lvc_test")
-
-    cache = GroupingLatestValueCache(channel.new_receiver(), key=lambda x: x[0])
-    sender = channel.new_sender()
-
-    assert cache.get(6) is None
-    assert 6 not in cache
-
-    await sender.send((6, "twenty-six"))
-
-    assert 6 in cache
-    assert cache.get(6) == (6, "twenty-six")
-
-    await cache.stop()
-    ```
-"""
+"""The GroupingLatestValueCache caches the latest values in a receiver grouped by key."""
 
 
 import asyncio
@@ -59,7 +23,43 @@
 
 
 class GroupingLatestValueCache(Mapping[HashableT, ValueT_co]):
-    """A cache that stores the latest value in a receiver, grouped by key."""
+    """A cache that stores the latest value in a receiver, grouped by key.
+
+    It provides a way to look up on demand, the latest value in a stream for any key, as
+    long as there has been at least one value received for that key.
+
+    [GroupingLatestValueCache][frequenz.channels.experimental.GroupingLatestValueCache]
+    takes a [Receiver][frequenz.channels.Receiver] and a `key` function as arguments and
+    stores the latest value received by that receiver for each key separately.
+
+    The `GroupingLatestValueCache` implements the [`Mapping`][collections.abc.Mapping]
+    interface, so it can be used like a dictionary. It is not
+    a [`MutableMapping`][collections.abc.MutableMapping] because users can't mutate the
+    cache directly, it is only mutated by the underlying receiver. There is one exception
+    though, users can clear individual keys from the cache using the
+    [clear][frequenz.channels.experimental.GroupingLatestValueCache.clear] method.
+
+    Example:
+        ```python
+        from frequenz.channels import Broadcast
+        from frequenz.channels.experimental import GroupingLatestValueCache
+
+        channel = Broadcast[tuple[int, str]](name="lvc_test")
+
+        cache = GroupingLatestValueCache(channel.new_receiver(), key=lambda x: x[0])
+        sender = channel.new_sender()
+
+        assert cache.get(6) is None
+        assert 6 not in cache
+
+        await sender.send((6, "twenty-six"))
+
+        assert 6 in cache
+        assert cache.get(6) == (6, "twenty-six")
+
+        await cache.stop()
+        ```
+    """
 
     def __init__(
         self,