Database as a context manager, fixed many pytest warnings

* Database can now work as a context manager
* Claude Code helped fix a ton of .close() warnings

https://gistpreview.github.io/?730f0c5dc38528a1dd0615f330bd5481

* New autouse fixture to help with test warnings

Refs https://github.com/simonw/sqlite-utils/issues/692#issuecomment-3644371889

* Fix all remaining resource warnings

https://gistpreview.github.io/?0bb8e869b82f6ff0db647de755182502

Closes #692

sqlite_utils/db.py

@@ -382,6 +382,12 @@ class Database:
             pm.hook.prepare_connection(conn=self.conn)
         self.strict = strict
 
+    def __enter__(self) -> "Database":
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+        self.close()
+
     def close(self) -> None:
         "Close the SQLite connection, and the underlying database file"
         self.conn.close()