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_analyze_tables.py

@@ -137,6 +137,7 @@ def db_to_analyze_path(db_to_analyze, tmpdir):
     db = sqlite3.connect(path)
     sql = "\n".join(db_to_analyze.iterdump())
     db.executescript(sql)
+    db.close()
     return path