Bundle cp313 and cp314 pygame for ROCKNIX Python 3.14

[misantronic]

Fixes #127.

ROCKNIX nightly 20260822 ships Python 3.14, while the bundle vendors a pygame-ce wheel whose extension modules are tagged cpython-313. An interpreter never loads extensions built for another minor version, so pygame/__init__.py (pure Python) imports fine and then dies on from pygame.base import *.

The two aarch64 wheels of pygame-ce 2.5.7 merge cleanly: their pure-Python files are identical and their pygame_ce.libs payloads are byte-for-byte the same, so base.cpython-313-*.so and base.cpython-314-*.so can sit side by side and each interpreter picks its own. That covers stable ROCKNIX and the nightlies from one bundle, with no launcher or install-time detection.

• fetch_vendor.sh (new) downloads both wheels and merges them into vendor/, matching the pattern the onion and muos ports already use.
• build_bundle.sh refuses to build unless every ABI in REQUIRED_PY_VERSIONS is present in the vendor directory.
• README documents the multi-ABI rule and how to add a future Python version.

Installer grows 17.4 MB to 19.1 MB. Devices on Python 3.13 receive byte-identical files to alpha1, the cp314 modules are purely additive. Verified locally that the built payload contains both ABI sets; on-device confirmation for 3.14 is pending with the issue reporter.