Auto-install pinned Zig toolchain in setup + devcontainer (#34) #91

Job	Run time
rust-ci / Detect Cargo.toml	4s
rust-ci / Cargo check + clippy + fmt	7s
rust-ci / Cargo audit (security)	0s
rust-ci / Coverage (tarpaulin + codecov)	0s
rust-ci / Cargo test	0s
	11s

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