gh-127681: Fix overflow vulnerabilities in PyMem_Malloc calls #3394

Job	Run time
x86_64-apple-darwin/clang	14m 41s
aarch64-unknown-linux-gnu/gcc	6m 23s
aarch64-apple-darwin/clang	12m 25s
x86_64-unknown-linux-gnu/gcc-free-threading	7m 21s
x86_64-unknown-linux-gnu/gcc	10m 14s
	51m 4s

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