WIP: feat: add `update-backlog` subcmd. #19

Job	Run time
block-autosquash-commits	0s
cargo-deny	20s
Clippy (stable)	38s
Check (ubuntu-latest, stable)	28s
Clippy (beta)	34s
Check (ubuntu-latest, beta)	31s
Check (windows-latest, stable)	27s
Rustfmt (stable)	9s
Documentation (stable)	36s
Check (windows-latest, beta)	27s
Documentation (beta)	1m 7s
Test Suite (ubuntu-latest, stable)	37s
Check (macOS-latest, stable)	29s
Test Suite (ubuntu-latest, beta)	40s
Check (macOS-latest, beta)	33s
Test Suite (windows-latest, stable)	35s
Test Suite (windows-latest, beta)	38s
Test Suite (macOS-latest, stable)	42s
Test Suite (macOS-latest, beta)	42s
	10m 13s

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