gh-140009: Replace PyTuple_Pack with PyTuple_FromArray in _warnings

[andrewloux]

Replaces PyTuple_Pack(N, ...) calls with PyTuple_FromArray() in Python/_warnings.c, avoiding variadic function call overhead.

Four call sites converted (2-element, 3-element, and 5-element tuples). PyTuple_Pack(1, ...) calls are not present in this file.

Part of #140009.

• Issue: Improve performance by replacing PyTuple_Pack with PyTuple_FromArray #140009

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[andrewloux]

Closing since the pyperf numbers I posted above don’t show a measurable improvement (benchmarks within noise / not significant). Happy to reopen / redo with a different benchmark methodology if maintainers think this is still worth taking for Python/_warnings.c.