[stubtest] support `@type_check_only` decorator #11554

Job	Run time
Test mypyc suite with 32-bit Python	10m 35s
Test suite with py38-ubuntu, mypyc-compiled	29m 38s
Test suite with py38-windows-64	27m 39s
Test suite with py39-ubuntu	32m 52s
Test suite with py310-ubuntu	18m 55s
Test suite with py311-ubuntu, mypyc-compiled	18m 2s
Test suite with py312-ubuntu, mypyc-compiled	25m 15s
mypyc runtime tests with py39-macos	4m 32s
mypyc runtime tests with py38-debug-build-ubuntu	5m 17s
Type check our own code (py38-ubuntu)	1m 45s
Type check our own code (py38-windows-64)	3m 50s
Formatting and code style with Black + ruff	47s
	2h 59m 7s

Provide feedback