Tests

Add more test cases for type narrowing #20172

Job	Run time
Test mypyc suite with 32-bit Python	9m 44s
Test suite with py314t-ubuntu, mypyc-compiled	17m 11s
Test suite with py314-ubuntu, mypyc-compiled	14m 40s
Test suite with py311-ubuntu	9m 42s
mypyc runtime tests with py310-ubuntu	5m 29s
Test suite with py314-windows-64	27m 25s
Parallel tests with py314-ubuntu, interpreted	24m 33s
Test suite with py312-ubuntu	10m 15s
Test suite with py313-ubuntu, mypyc-compiled	14m 40s
Test suite with py310-ubuntu, mypyc-compiled	15m 37s
mypyc runtime tests with py313-macos	6m 29s
Type check our own code (py310-ubuntu)	1m 42s
Type check our own code (py310-windows-64)	2m 36s
Parallel tests with py314-ubuntu, mypyc-compiled	28m 13s
Formatting and code style with Black + ruff	1m 54s
	3h 10m 10s

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