gh-140009: Optimize dict object by replacing PyTuple_Pack with PyTuple_FromArray

[rashes2006]

Fixes: #144529

Summary

This PR replaces PyTuple_Pack with PyTuple_FromArray in Objects/dictobject.c for creating small tuples (size 2).

PyTuple_FromArray is more efficient than PyTuple_Pack because it avoids the overhead of variadic arguments (va_args) processing by taking a pointer to a pre-allocated array of PyObject*.

Changes

• dictiter_new: Replaced PyTuple_Pack(2, Py_None, Py_None) with PyTuple_FromArray using a stack-allocated array.
• dictitems_xor_lock_held: Replaced PyTuple_Pack(2, key, val2) with PyTuple_FromArray.

Performance Impact

This is part of a general effort to optimize small tuple creation across the codebase. Replacing PyTuple_Pack with PyTuple_FromArray for small, fixed-size tuples reduces call overhead.

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

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