Close DB connection when Database is garbage collected

Register a weakref.finalize callback to close the underlying DB
connection when the Database instance is garbage collected.

This address a ResourceWarning which was introduced in Python 3.13
(python/cpython#105539).

Author: mbhutton

things/database.py

@@ -10,6 +10,7 @@
 import sqlite3
 from textwrap import dedent
 from typing import Optional, Union
+import weakref
 
 
 # --------------------------------------------------
@@ -186,6 +187,7 @@ def __init__(self, filepath=None, print_sql=False):
         # See: https://sqlite.org/uri.html#recognized_query_parameters
         uri = f"file:{self.filepath}?mode=ro"
         self.connection = sqlite3.connect(uri, uri=True)  # pylint: disable=E1101
+        self._finalizer = weakref.finalize(self, self._close_connection)
 
         # Test for migrated database in Things 3.15.16+
         # --------------------------------
@@ -510,6 +512,10 @@ def execute_query(self, sql_query, parameters=(), row_factory=None):
 
             return cursor.fetchall()
 
+    def _close_connection(self):
+        """Close the database connection."""
+        self.connection.close()
+
 
 # Helper functions