list-ops: add exercise #2789

Job	Run time
configlet lint	3s
markdown lint	8s
Clippy	7s
Check compilation (stable)	15s
Check exercises on nightly (benchmark enabled)	10s
Check compilation (beta)	13s
Check Rust Formatting	37s
Run shellcheck on scripts	5s
Run repository tests	20s
	1m 58s

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