gh-144412: Require tuple args in pickle REDUCE

[sabasiddique1]

Summary

• Require tuple args in pickle.load_reduce() to match _pickle
• Add regression test for non-tuple REDUCE args

• Issue: Python pickle load_reduce function doesn't check if args is a tuple #144412

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[da-woods]

Can you explain what this test adds?

[sabasiddique1]

NR. case ensures that when REDUCE receives a non-tuple args, pickle.load_reduce() raises TypeError consistently (matching _pickle) and prevents regressions in this validation.

[da-woods]

Could you look carefully at the surrounding code and explain what this test adds?

[sabasiddique1]

Surrounding tests already cover an invalid callable (N)R.) and a valid REDUCE call with tuple args (int + ()).
cbuiltins\nint\nNR. is different because the callable is valid, but the REDUCE args object is not a tuple (None), so it reaches load_reduce() and hits the new gh-144412 tuple check.
This confirms we raise TypeError at the correct point, consistent with _pickle.
It also acts as a regression test to ensure non-tuple REDUCE args aren’t accidentally accepted again.