Add c binding to `voronoi_compute_neighbors_c` (#21) #76

Job	Run time
ubuntu-latest - gfortran-11 - regular - push	7s
ubuntu-latest - gfortran-13 - regular - push	10s
macos-latest - gfortran-11 - regular - push	22s
macos-latest - gfortran-13 - regular - push	22s
windows-latest - gfortran - regular - push	2m 12s
ubuntu-latest - gfortran-13 - coverage - push	21s
	3m 34s

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