lang/python315: New port, Python 3.15.0beta1

Please read: https://blog.python.org/2026/05/python-3150-beta-1/
Changelog: https://www.python.org/downloads/release/python-3150b1/
Details: https://docs.python.org/3.15/whatsnew/3.15.html

PR: 295131
Sponsored by: UNIS Labs