fix(pkg-py): .server() now returns reactives, making them truly session-specific (#116)

* fix(pkg-py): .server() now returns reactives, making them truly session-specific

* Apply suggestions from code review

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: cpsievert

pkg-py/src/querychat/datasource.py renamed to pkg-py/src/querychat/_datasource.py

@@ -11,7 +11,7 @@
     import sqlalchemy
     from narwhals.stable.v1.typing import IntoFrame
 
-    from .datasource import DataSource
+    from ._datasource import DataSource
 
 
 def init(