Templatize spreadinterp and more cleanups #372

Job	Run time
prepare	5s
Build with Pip (ubuntu-22.04, 3.8, llvm, -march=native)	1m 32s
Build with Pip (ubuntu-22.04, 3.8, llvm, -march=x86-64)	1m 11s
Build with Pip (ubuntu-22.04, 3.8, gcc, -march=native)	53s
Build with Pip (ubuntu-22.04, 3.8, gcc, -march=x86-64)	54s
Build with Pip (ubuntu-22.04, 3.11, llvm, -march=native)	1m 12s
Build with Pip (ubuntu-22.04, 3.11, llvm, -march=x86-64)	1m 9s
Build with Pip (ubuntu-22.04, 3.11, gcc, -march=native)	51s
Build with Pip (ubuntu-22.04, 3.11, gcc, -march=x86-64)	51s
Build with Pip (windows-2022, 3.8, msvc, /arch:AVX2)	11m 46s
Build with Pip (windows-2022, 3.8, msvc, /arch:SSE2)	11m 48s
Build with Pip (windows-2022, 3.8, llvm, /arch:AVX2)	13m 31s
Build with Pip (windows-2022, 3.8, llvm, /arch:SSE2)	11m 59s
Build with Pip (windows-2022, 3.11, msvc, /arch:AVX2)	12m 38s
Build with Pip (windows-2022, 3.11, msvc, /arch:SSE2)	12m 42s
Build with Pip (windows-2022, 3.11, llvm, /arch:AVX2)	11m 56s
Build with Pip (windows-2022, 3.11, llvm, /arch:SSE2)	13m 0s
Build with Pip (macos-13, 3.8, llvm, -march=native)	4m 47s
Build with Pip (macos-13, 3.8, llvm, -march=x86-64)	2m 51s
Build with Pip (macos-13, 3.8, gcc-14, -march=native)	1m 50s
Build with Pip (macos-13, 3.8, gcc-14, -march=x86-64)	1m 55s
Build with Pip (macos-13, 3.11, llvm, -march=native)	4m 51s
Build with Pip (macos-13, 3.11, llvm, -march=x86-64)	5m 7s
Build with Pip (macos-13, 3.11, gcc-14, -march=native)	2m 9s
Build with Pip (macos-13, 3.11, gcc-14, -march=x86-64)	2m 6s
	2h 13m 34s

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