Tests

Initial implementation of parallel type checking #19568

Job	Run time
Test mypyc suite with 32-bit Python	9m 4s
Test suite with py314-ubuntu, mypyc-compiled	14m 2s
Test suite with py314-windows-64	26m 44s
Parallel tests with py314-ubuntu, interpreted	22m 35s
mypyc runtime tests with py313-macos	4m 33s
Test suite with py312-ubuntu	9m 44s
Parallel tests with py314-ubuntu, mypyc-compiled	27m 37s
Type check our own code (py310-windows-64)	2m 22s
Formatting and code style with Black + ruff	2m 14s
Test suite with py313-ubuntu, mypyc-compiled	13m 47s
Test suite with py310-ubuntu, mypyc-compiled	13m 57s
Test suite with py311-ubuntu	8m 59s
Type check our own code (py310-ubuntu)	1m 34s
mypyc runtime tests with py310-ubuntu	5m 6s
	2h 42m 18s

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