bip-0069: Fix Python 3 compatibility by replacing deprecated cmp para…

[strmfos]

Replace deprecated cmp parameter in sorted() calls with key=cmp_to_key() to fix Python 3 compatibility. The cmp parameter was removed in Python 3.0.

• Use functools.cmp_to_key() as the official migration path
• Maintains identical sorting behavior across Python versions
• Fixes: TypeError: 'cmp' is an invalid keyword argument for sorted()

[jonatack]

Thank you @strmfos for your proposal. However, it is a duplicate of #1943 that goes further (don't hesitate to review it!), so closing here for now.