[mypyc] Promotion to Value Type optimization #13967

Job	Run time
Test mypyc suite with 32-bit Python	7m 10s
Test suite with py38-ubuntu, mypyc-compiled	18m 21s
Test suite with py38-windows-64	20m 49s
Test suite with py39-ubuntu	17m 31s
Test suite with py310-ubuntu	16m 37s
Test suite with py311-ubuntu, mypyc-compiled	16m 29s
Test suite with py312-ubuntu, mypyc-compiled	18m 28s
Test suite with py313-ubuntu, mypyc-compiled	19m 10s
mypyc runtime tests with py39-macos	4m 53s
Type check our own code (py38-ubuntu)	1m 52s
Type check our own code (py38-windows-64)	2m 21s
Formatting and code style with Black + ruff	59s
	2h 24m 40s

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