gh-145192: Improve performance of PySequence_GetSlice #3063

Job	Run time
aarch64-apple-darwin/clang	3m 9s
aarch64-unknown-linux-gnu/gcc	2m 11s
x86_64-apple-darwin/clang	7m 37s
x86_64-unknown-linux-gnu/gcc-free-threading	2m 6s
x86_64-unknown-linux-gnu/gcc	2m 2s
	17m 5s

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