* Align base64 encodings with Python 3.15
Accept hexlify keyword arguments and migrate base64 and its tests directly from CPython v3.15.0 using update_lib.
Assisted-by: OpenAI Codex:model version unavailable
* Update Hypothesis fallback for multi-argument examples
Import the CPython 3.15 final fallback helper with scripts/update_lib migrate. Keep canonical base64 round-trip examples unchanged while passing their positional arguments as one subTest message.
Validation: six canonical base64 methods, fourteen fixed examples; bounded source-only runs with the existing same-native PR binary.
Assisted-by: OpenAI Codex:model version unavailable