Use np.int64 type for day to nanosecond conversion (NEP50) (#922) #514

Job	Run time
Test wheel (numpy~=1.23 + ubuntu-22.04)	3m 14s
Test wheel (numpy~=1.23 + ubuntu-22.04)	3m 14s
Test wheel (numpy~=1.24 + ubuntu-22.04)	3m 7s
Test wheel (numpy~=1.24 + ubuntu-22.04)	3m 7s
Test wheel (numpy~=1.25 + ubuntu-22.04)	3m 3s
Test wheel (numpy~=1.25 + ubuntu-22.04)	3m 3s
Test wheel (numpy#latest + ubuntu-22.04)	1s
Test wheel (numpy#latest + ubuntu-22.04)	3m 27s
Test wheel (numpy~=1.23 + windows-2019)	6m 17s
Test wheel (numpy~=1.23 + windows-2019)	6m 17s
Test wheel (numpy~=1.24 + windows-2019)	5m 18s
Test wheel (numpy~=1.24 + windows-2019)	5m 18s
Test wheel (numpy~=1.25 + windows-2019)	4m 56s
Test wheel (numpy~=1.25 + windows-2019)	4m 56s
Test wheel (numpy#latest + windows-2019)	5m 9s
Test wheel (numpy#latest + windows-2019)	5m 9s
	1h 5m 36s

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