refactor(sqlite): add check_cursor_valid method for cursor state validation by ever0de · Pull Request #6342 · RustPython/RustPython

…dation

Extract cursor validity check into a separate method that doesn't hold
the lock. This is useful for executescript which only needs to verify
the cursor state but doesn't need to modify CursorInner.

- Add check_cursor_valid() method that checks if cursor is initialized
  and not closed without retaining the mutex guard
- Use check_cursor_valid() in executescript instead of inner() since
  executescript doesn't modify CursorInner