build(version): bump to 3.0.0a2, update cross-deps and PyPI metadata

Author: dekoza

src/getpaid_przelewy24/__init__.py

@@ -3,7 +3,7 @@
 # Lazy imports — client and processor are defined in later tasks.
 # This avoids ImportError when only types.py is implemented so far.
 
-__version__ = "0.1.2"
+__version__ = "3.0.0a2"
 
 __all__ = [
     "P24Client",