Rust

limit `concurrent_task` to `executor_cores` #207

Job	Run time
Lint	18s
Build Libraries on AMD64 Rust stable	13m 58s
Test on windows-latest Rust stable	6m 54s
Test on macos-latest Rust stable	3m 38s
Test Workspace on AMD64 Rust stable	8m 20s
Check Cargo.toml formatting (amd64, stable)	1m 39s
Clippy (amd64, stable)	3m 16s
Test Ballista on AMD64 Rust stable	5m 27s
Docker	22s
verify benchmark results (amd64) (amd64, stable)	10m 50s
	54m 42s

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