Fix cython syntax, add tests #317

Job	Run time
build (Debug, yes, 3.12, yes, ubuntu-20.04, gcc)	3m 39s
build (Debug, yes, 3.11, yes, ubuntu-20.04, gcc)	3m 28s
build (Debug, yes, 3.10, yes, ubuntu-20.04, gcc)	3m 57s
build (Debug, yes, 3.9, yes, ubuntu-20.04, gcc)	3m 33s
build (Release, 3.8, yes, ubuntu-20.04, gcc)	4m 36s
build (Release, 3.8, yes, gmpxx, no, ubuntu-20.04, gcc)	4m 35s
build (Release, 3.8, yes, ubuntu-20.04, gcc)	4m 35s
build (Release, yes, 3.8, ubuntu-20.04, gcc)	4m 38s
build (Release, 3.9, yes, ubuntu-20.04, gcc)	4m 26s
build (Release, 3.9, yes, flint, yes, ubuntu-20.04, gcc)	4m 52s
build (Debug, 3.8, yes, yes, ubuntu-20.04, clang)	3m 45s
build (Release, 3.8, yes, ubuntu-20.04, clang)	4m 24s
build (Debug, 3.10, yes, 14, yes, boostmp, -k "not integer_nthroot", ubuntu-22.04, deb http://apt...	5m 32s
build (Debug, 3.8, yes, 5, macos-latest, clang)	11m 58s
build (Release, 3.9, no, macos-latest, clang)	8m 55s
build (Debug, 3.8, no, macos-latest, gcc)	7m 55s
build (Release, 3.8, macos-latest, gcc)	9m 49s
build (Release, 3.8, ubuntu-20.04, yes, yes, yes, yes, yes, flint, yes, gcc)	4m 40s
	1h 39m 17s

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