Implement lowercase

[varnerac]

The Erlang implementation of lowercase does not implement all of the Unicode rules for lowercasing.

See https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-3/#G54277

In addition to fixing shortfalls in the Erlang lowercase methods:

1> string:lowercase(<<"ΒόλοΣ"/utf8>>).
<<"βόλοσ"/utf8>>
2> string:casefold(<<"ΒόλοΣ"/utf8>>).
<<"βόλοσ"/utf8>>

which should produce βόλος like:

Python 3.13.5 (main, Jun 11 2025, 15:36:57) [Clang 17.0.0 (clang-1700.0.13.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> "ΒόλοΣ".lower()
'βόλος'

This also let's us use a Unicode version independent of the underlying Erlang (or Javascript) runtime.