[mypyc] Inline fast paths of integer unboxing operations #12417

Job	Run time
Test mypyc suite with 32-bit Python	6m 9s
Test suite with py38-ubuntu, mypyc-compiled	6m 31s
Test suite with py38-windows-64	18m 4s
Test suite with py39-ubuntu	15m 24s
Test suite with py310-ubuntu	14m 41s
Test suite with py311-ubuntu, mypyc-compiled	5m 1s
Test suite with py312-ubuntu, mypyc-compiled	18m 30s
mypyc runtime tests with py39-macos	3m 2s
mypyc runtime tests with py38-debug-build-ubuntu	3m 39s
Type check our own code (py38-ubuntu)	1m 52s
Type check our own code (py38-windows-64)	2m 12s
Formatting and code style with Black + ruff	42s
	1h 35m 47s

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