Convert get-subsystem-split to git-subsystem-split.py

[peterbarker]

Thanks ChatGPT!

Perhaps we have this as an alternative for testing for some time, then rename it over the existing shell script.

[tpwrules]

argparse supports all of the manually-implemented argument logic, e.g. https://docs.python.org/3/library/argparse.html#mutual-exclusion

[peterbarker]

argparse supports all of the manually-implemented argument logic, e.g. https://docs.python.org/3/library/argparse.html#mutual-exclusion

I assure you no logic in this PR was made manually.

I want agreement that we'll do this before working on it.

[tpwrules]

Sure, I'd approve more Python over Bash. This would let us address various limitations more easily and testably. But I would not deign to approve stuff written by ChatGPT ;)

[peterbarker]

But I would not deign to approve stuff written by ChatGPT ;)

Which is why I clearly marked this as such and said it needed more testing :-)

OTOH, it appears to have done a damned good job on first inspection (OTGH that's often the case with this stuff!).

[tridge]

I'd definitely like to see it in python