Fix sqlite Cursor initialization check by ever0de · Pull Request #6198 · RustPython/RustPython

Add proper __init__ validation for sqlite3.Cursor to ensure base class
__init__ is called before using cursor methods. This fixes the
test_cursor_constructor_call_check test case.

Changes:
- Modified Cursor to initialize with inner=None in py_new
- Added explicit __init__ method that sets up CursorInner
- Updated close() method to check for uninitialized state
- Changed error message to match CPython: 'Base Cursor.__init__ not called.'

This ensures CPython compatibility where attempting to use a Cursor
instance without calling the base __init__ raises ProgrammingError.