[mypyc] Promotion to Value Type optimization #13961

Job	Run time
Test mypyc suite with 32-bit Python	7m 9s
Test suite with py38-ubuntu, mypyc-compiled	18m 4s
Test suite with py38-windows-64	20m 41s
Test suite with py39-ubuntu	18m 14s
Test suite with py310-ubuntu	16m 22s
Test suite with py311-ubuntu, mypyc-compiled	16m 11s
Test suite with py312-ubuntu, mypyc-compiled	18m 17s
Test suite with py313-ubuntu, mypyc-compiled	18m 40s
mypyc runtime tests with py39-macos	5m 0s
Type check our own code (py38-ubuntu)	1m 52s
Type check our own code (py38-windows-64)	2m 13s
Formatting and code style with Black + ruff	53s
	2h 23m 36s

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