stubgen: add support for PEPs 695 and 696 syntax (#18054) #13763

Job	Run time
Test suite with py38-ubuntu, mypyc-compiled	17m 43s
Test mypyc suite with 32-bit Python	7m 48s
Test suite with py38-windows-64	19m 33s
Test suite with py39-ubuntu	16m 26s
Test suite with py310-ubuntu	15m 26s
Test suite with py311-ubuntu, mypyc-compiled	15m 38s
Test suite with py312-ubuntu, mypyc-compiled	17m 59s
Test suite with py313-ubuntu, mypyc-compiled	18m 18s
mypyc runtime tests with py39-macos	4m 38s
Type check our own code (py38-ubuntu)	1m 58s
Type check our own code (py38-windows-64)	2m 40s
Formatting and code style with Black + ruff	33s
	2h 18m 40s

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