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

tests/test_cli.py

@@ -19,9 +19,11 @@ def _supports_pragma_function_list():
     db = Database(memory=True)
     try:
         db.execute("select * from pragma_function_list()")
+        return True
     except Exception:
         return False
-    return True
+    finally:
+        db.close()
 
 
 def _has_compiled_ext():