Rust

limit `concurrent_task` to `executor_cores` #209

Job	Run time
Build Libraries on AMD64 Rust stable	15m 1s
Test on windows-latest Rust stable	7m 31s
Lint	21s
Test on macos-latest Rust stable	3m 31s
Test Ballista on AMD64 Rust stable	5m 41s
Clippy (amd64, stable)	3m 10s
Docker	14s
Check Cargo.toml formatting (amd64, stable)	1m 33s
Test Workspace on AMD64 Rust stable	8m 12s
verify benchmark results (amd64) (amd64, stable)	10m 47s
	56m 1s

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