Clean documentation and add type hints #1473

Job	Run time
get-commit-message	3s
test-gpu (cufinufft)	14m 53s
test-cpu (finufft)	19m 24s
test-gpu (gpunufft)	15m 45s
test-cpu (pynfft)	4m 42s
test-gpu (torchkbnufft-gpu)	15m 35s
test-cpu (sigpy)	4m 47s
test-examples	23m 8s
Build API Documentation	0s
coverage	26s
Compile the coverage badge in docs	0s
	1h 38m 43s

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