WIP: feat: add `update-backlog` subcmd. #277

Job	Run time
Clippy (stable)	39s
cargo-deny	23s
Check (ubuntu-latest, stable)	33s
Rustfmt (stable)	12s
Check (ubuntu-latest, beta)	32s
Clippy (beta)	37s
Test Suite (ubuntu-latest, stable)	54s
Check (windows-latest, stable)	1m 45s
Test Suite (ubuntu-latest, beta)	57s
Check (windows-latest, beta)	1m 19s
Test Suite (windows-latest, stable)	58s
Test Suite (windows-latest, beta)	59s
Check (macOS-latest, stable)	48s
Test Suite (macOS-latest, stable)	55s
Check (macOS-latest, beta)	40s
Test Suite (macOS-latest, beta)	1m 0s
	13m 11s

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