Rust

Specify rust toolchain explicitly, document how to change it #4445

Job	Run time
Check cargo fmt	41s
Check License Header	2m 43s
linux build test	5m 2s
build with wasm-pack	3m 44s
cargo test (macos-aarch64)	13m 35s
Verify MSRV (Min Supported Rust Version)	8m 14s
Verify Vendored Code	53s
cargo check no default features	8m 23s
cargo test (amd64)	15m 50s
cargo check functions	2m 21s
cargo check datafusion	5m 16s
cargo test doc (amd64)	18m 36s
cargo doc	4m 5s
cargo examples (amd64)	17m 16s
Run sqllogictest with Postgres runner	6m 0s
cargo test pyarrow (amd64)	6m 46s
verify benchmark results (amd64)	10m 20s
check Cargo.toml formatting	4m 6s
clippy	6m 50s
check configs.md and ***_functions.md is up-to-date	5m 8s
	2h 25m 49s

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