Speed up time stretching ~3x on Linux with FFTW3. #1176

Job	Run time
Pre-build on macos-13 with clang	3m 8s
Lint C++	17m 2s
Lint Python (3.12, ubuntu-20.04)	11s
Pre-build on ubuntu-20.04 with gcc	8m 26s
Pre-build on ubuntu-20.04 with clang	10m 4s
Test 1 / 8 with Python 3.12 on ubuntu-20.04	1m 14s
Test 2 / 8 with Python 3.12 on ubuntu-20.04	1m 12s
Test with Python 3.7 on macos-13	2m 46s
Test 3 / 8 with Python 3.12 on ubuntu-20.04	1m 12s
Test with Python 3.8 on macos-13	2m 57s
Test 4 / 8 with Python 3.12 on ubuntu-20.04	1m 24s
Test 5 / 8 with Python 3.12 on ubuntu-20.04	1m 8s
Test with Python 3.9 on macos-13	3m 0s
Test 6 / 8 with Python 3.12 on ubuntu-20.04	1m 10s
Test with Python 3.10 on macos-13	3m 1s
Test 7 / 8 with Python 3.12 on ubuntu-20.04	1m 26s
Test with Python 3.11 on macos-13	2m 59s
Test with Python 3.12 on macos-13	2m 59s
Test 8 / 8 with Python 3.12 on ubuntu-20.04	1m 24s
Test with Python 3.7 on ubuntu-20.04	2m 57s
Test with Python 3.8 on ubuntu-20.04	2m 59s
Test with Python 3.9 on ubuntu-20.04	2m 58s
Test with Python 3.10 on ubuntu-20.04	2m 59s
Test with Python 3.11 on ubuntu-20.04	2m 58s
Test with Python 3.12 on ubuntu-20.04	2m 56s
Test with Python 3.12 on windows-latest	2m 38s
Test with Python 3.7 + Address Sanitizer	4m 12s
Test with Python 3.8 + Address Sanitizer	4m 29s
Test with Python 3.9 + Address Sanitizer	4m 29s
Test with Python 3.10 + Address Sanitizer	4m 29s
Test with Python 3.11 + Address Sanitizer	4m 22s
Build wheel for ${{ matrix.build }}	0s
Upload wheels to PyPI	0s
	1h 49m 9s

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