Remove itertools dependency #215

Job	Run time
linux (aarch64-unknown-linux-gnu)	3m 45s
windows (x86_64-pc-windows-msvc, x64)	6m 22s
macos (x86_64, x64)	2m 49s
macos (aarch64, arm64)	2m 24s
windows (aarch64-pc-windows-msvc, x64)	5m 34s
linux (x86_64-unknown-linux-gnu)	3m 20s
sdist	2m 51s
Test with Python 3.12	5s
Test with Python 3.14	7s
Merge artifacts	4s
	27m 21s

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