Ship PEP 561 py.typed markers so the connector's inline type hints reach downstream users

The connector is fully type-annotated, but per PEP 561 a type checker ignores an installed package's inline hints unless it ships a py.typed marker. so pip install mariadb users (and cross-package checks of mariadb_shared) see everything as Any.

fix: Add empty py.typed files to each packages and ship them via package-data in every wheel.