Add `huak-toolchain` (first-pass) #422

Job	Run time
Build with maturin	2m 20s
Clippy lints	28s
Build and test (ubuntu-latest)	1m 1s
Formatting check	19s
Build and test (windows-latest)	1m 4s
Build and test (macos-latest)	1m 3s
	6m 15s

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