Fix duplicate attribute docs in SessionExtensionComponents

The docs build runs Sphinx with --fail-on-warning. SessionExtensionComponents
documented its fields in both a napoleon `Attributes:` section and the dataclass
class-body annotations, so autoapi emitted each field twice and the build failed
with six "duplicate object description" warnings.

Move each field's description to a per-field docstring under its annotation so
autoapi renders exactly one entry per field.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

python/datafusion/context.py

diff --git a/python/datafusion/context.py b/python/datafusion/context.py
index 19b3191..9d68fec 100644
--- a/python/datafusion/context.py
+++ b/python/datafusion/context.py
@@ -165,23 +165,24 @@
     must be created against the context passed to that method; components bound
     to any other context hold a task-context provider for the wrong session and
     cannot be rebound.
-
-    Attributes:
-        logical_extension_codecs: Logical codecs to add to the session's codec
-            chain, in declaration order.
-        physical_extension_codecs: Physical codecs to add to the session's
-            codec chain, in declaration order.
-        query_planner: Optional query planner. At most one extension per
-            :py:meth:`SessionContext.with_extensions` call may supply one.
     """
 
     logical_extension_codecs: tuple[
         LogicalExtensionCodecExportable | _PyCapsule, ...
     ] = ()
+    """Logical codecs to add to the session's codec chain, in declaration order."""
+
     physical_extension_codecs: tuple[
         PhysicalExtensionCodecExportable | _PyCapsule, ...
     ] = ()
+    """Physical codecs to add to the session's codec chain, in declaration order."""
+
     query_planner: QueryPlannerExportable | _PyCapsule | None = None
+    """Optional query planner.
+
+    At most one extension per :py:meth:`SessionContext.with_extensions` call may
+    supply one.
+    """
 
 
 class SessionExtensionExportable(Protocol):