Convert NodePtr to a newtype rather than alias #1498

Job	Run time
Wheel on macos-latest py-3.7	4m 46s
Wheel on ubuntu-latest py-3.7	3m 36s
Wheel on windows-latest py-3.7	5m 10s
Checks	1m 11s
coverage	22m 7s
Run fuzz targets (macos-latest, 3.7)	38m 55s
Run fuzz targets (ubuntu-latest, 3.7)	26m 59s
Unit tests (macos-latest, 3.7)	8m 24s
Unit tests (ubuntu-latest, 3.7)	4m 59s
Unit tests (windows-latest, 3.7)	7m 37s
	2h 3m 44s

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