Speed up copy.deepcopy() of containers holding atomic elements

copy.deepcopy() copies a structure by sending every element back through deepcopy(). For elements that need no copying at all — strings, ints, None, booleans, floats and the other immutable atomic types — that round trip still costs a function call each, even though the value handed back is the same object.

Real data is dominated by these atomic leaves. A parsed JSON document, a settings dict cloned before mutation, a record copied inside a framework: the keys are strings and most values are strings and numbers. Copying such a structure spends most of its time calling deepcopy() only to receive the same object straight back.

Deep-copying 105 JSON documents drawn from the top-1000 PyPI projects takes 1.20 ms today. Folding the atomic-type check into the dict, list and tuple copiers brings that to 970 µs, 23% faster, with identical handling of shared references, recursive structures and int/tuple subclasses.

Linked PRs

• gh-150822

Start at the copy.deepcopy() entry point and inspect linked PR gh-150822, which indicates that work is already underway. Verify the reported optimization preserves shared references, recursive structures, and int/tuple subclass handling, while matching the stated benchmark improvement.