Add support for density compensation estimation with cufinufft #1481

Job	Run time
test-gpu (cufinufft)	3m 8s
get-commit-message	2s
test-cpu (finufft)	17m 9s
test-gpu (gpunufft)	3m 26s
test-cpu (pynfft)	4m 27s
test-gpu (torchkbnufft-gpu)	1s
test-cpu (sigpy)	4m 27s
test-examples	23m 36s
Build API Documentation	0s
coverage	24s
Compile the coverage badge in docs	0s
	56m 40s

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