mypy

gh-145219: Add Emscripten cross-build and clean configurability (#145… #19824

Job	Run time
Run mypy on Tools/build	17s
Run mypy on Lib/_pyrepl	24s
Run mypy on Lib/tomllib	18s
Run mypy on Tools/clinic	17s
Run mypy on Tools/peg_generator	20s
Run mypy on Tools/jit	20s
Run mypy on Lib/test/libregrtest	18s
Run mypy on Tools/cases_generator	17s
Run mypy on Tools/check-c-api-docs	16s
	2m 47s

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