Tests

Treat NotImplemented as a singleton type #20201

Job	Run time
Test mypyc suite with 32-bit Python	8m 53s
Test suite with py314t-ubuntu, mypyc-compiled	18m 7s
Parallel tests with py314-ubuntu, interpreted	25m 23s
Test suite with py314-ubuntu, mypyc-compiled	15m 5s
Test suite with py312-ubuntu	9m 47s
Test suite with py311-ubuntu	9m 30s
Test suite with py313-ubuntu, mypyc-compiled	14m 54s
Parallel tests with py314-ubuntu, mypyc-compiled	27m 33s
Type check our own code (py310-windows-64)	2m 43s
Formatting and code style with Black + ruff	1m 55s
Type check our own code (py310-ubuntu)	1m 37s
mypyc runtime tests with py313-macos	4m 46s
Test suite with py314-windows-64	27m 21s
mypyc runtime tests with py310-ubuntu	5m 31s
Test suite with py310-ubuntu, mypyc-compiled	14m 54s
	3h 7m 59s

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