please remove usage of future/past

[ZeroChaos-]

Gentoo has removed future due to upstream explicitly stating that it's dead

# Deprecated, doesn't work with python 3.12. Unmaintained with last
# serious release in 2019, and another release in 2024 that claims
# to support python 3.12 but fails tests if you actually do. No
# route to making it work with python 3.13 at all, and upstream
# explicitly states that future "like Python 2, is now done". The
# package is entirely redundant to packages not supporting python
# 2 anymore, and the ones that do support it should be using
# dev-python/six instead, anyways. Bug #888271

Multiple files in rflib still seem to import from past.builtins and past.utils which are part of future. Please refactor to not require these deprecated libraries.
https://python-future.org/whatsnew.html