Isolate all logic in _threadmodule #18

Job	Run time
i686-pc-windows-msvc/msvc (Debug)	16m 59s
i686-pc-windows-msvc/msvc (Release)	20m 36s
x86_64-pc-windows-msvc/msvc (Debug)	16m 47s
x86_64-pc-windows-msvc/msvc (Release)	22m 56s
x86_64-apple-darwin/clang (Debug)	17m 28s
x86_64-apple-darwin/clang (Release)	16m 24s
aarch64-apple-darwin/clang (Debug)	8m 37s
aarch64-apple-darwin/clang (Release)	12m 15s
x86_64-unknown-linux-gnu/gcc (Debug)	8m 5s
x86_64-unknown-linux-gnu/gcc (Release)	17m 48s
x86_64-unknown-linux-gnu/clang (Debug)	8m 12s
x86_64-unknown-linux-gnu/clang (Release)	13m 55s
aarch64-unknown-linux-gnu/gcc (Debug)	58m 26s
aarch64-unknown-linux-gnu/gcc (Release)	47m 13s
aarch64-unknown-linux-gnu/clang (Debug)	52m 22s
aarch64-unknown-linux-gnu/clang (Release)	30m 58s
	6h 9m 1s

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