Optimize find_shortest_chains #683

Job	Run time
Check Rust	1m 5s
benchmarks	6m 21s
Check Python 3.10, macos-latest	1m 16s
Check Python 3.9, windows-latest	2m 57s
Check Python 3.9, macos-latest	2m 10s
Check Python 3.12, macos-latest	1m 41s
Check Python 3.9, ubuntu-latest	1m 27s
Check Python 3.10, windows-latest	2m 49s
Check Python 3.11, macos-latest	1m 19s
Check Python 3.13-dev, macos-latest	2m 21s
Check Python 3.10, ubuntu-latest	1m 18s
Check Python 3.11, ubuntu-latest	1m 18s
Check Python 3.13-dev, ubuntu-latest	2m 17s
Check Python 3.12, windows-latest	3m 40s
Check Python 3.11, windows-latest	3m 14s
Check Python 3.12, ubuntu-latest	1m 26s
Check Python 3.13-dev, windows-latest	4m 30s
	41m 9s

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