Templatize spreadinterp and more cleanups #426

Job	Run time
prepare	5s
Build with Pip (ubuntu-22.04, 3.8, llvm, -march=native)	1m 17s
Build with Pip (ubuntu-22.04, 3.8, llvm, -march=x86-64)	1m 8s
Build with Pip (ubuntu-22.04, 3.8, gcc, -march=native)	55s
Build with Pip (ubuntu-22.04, 3.8, gcc, -march=x86-64)	1m 0s
Build with Pip (ubuntu-22.04, 3.11, llvm, -march=native)	1m 10s
Build with Pip (ubuntu-22.04, 3.11, llvm, -march=x86-64)	1m 2s
Build with Pip (ubuntu-22.04, 3.11, gcc, -march=native)	1m 3s
Build with Pip (ubuntu-22.04, 3.11, gcc, -march=x86-64)	59s
Build with Pip (windows-2022, 3.8, msvc, /arch:AVX2)	11m 14s
Build with Pip (windows-2022, 3.8, msvc, /arch:SSE2)	11m 46s
Build with Pip (windows-2022, 3.8, llvm, /arch:AVX2)	12m 43s
Build with Pip (windows-2022, 3.8, llvm, /arch:SSE2)	12m 31s
Build with Pip (windows-2022, 3.11, msvc, /arch:AVX2)	11m 55s
Build with Pip (windows-2022, 3.11, msvc, /arch:SSE2)	14m 9s
Build with Pip (windows-2022, 3.11, llvm, /arch:AVX2)	13m 43s
Build with Pip (windows-2022, 3.11, llvm, /arch:SSE2)	13m 12s
Build with Pip (macos-13, 3.8, llvm, -march=native)	3m 32s
Build with Pip (macos-13, 3.8, llvm, -march=x86-64)	2m 46s
Build with Pip (macos-13, 3.8, gcc-14, -march=native)	1m 45s
Build with Pip (macos-13, 3.8, gcc-14, -march=x86-64)	1m 40s
Build with Pip (macos-13, 3.11, llvm, -march=native)	2m 30s
Build with Pip (macos-13, 3.11, llvm, -march=x86-64)	4m 2s
Build with Pip (macos-13, 3.11, gcc-14, -march=native)	1m 37s
Build with Pip (macos-13, 3.11, gcc-14, -march=x86-64)	2m 2s
	2h 9m 46s

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