Support PEP-646 and PEP-692 in the same callable #11351

Job	Run time
Test mypyc suite with 32-bit Python	12m 34s
Test suite with py38-ubuntu, mypyc-compiled	24m 17s
Test suite with py38-windows-64	45m 27s
Test suite with py39-ubuntu	30m 19s
Test suite with py310-ubuntu	24m 32s
Test suite with py311-ubuntu, mypyc-compiled	21m 24s
Test suite with py312-ubuntu, mypyc-compiled	24m 34s
mypyc runtime tests with py38-macos	7m 36s
mypyc runtime tests with py38-debug-build-ubuntu	9m 34s
Type check our own code (py38-ubuntu)	2m 12s
Type check our own code (py38-windows-64)	3m 24s
Formatting and code style with Black + ruff	46s
	3h 26m 39s

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