Remove extra lookups and memory allocations from tsort graph construction #10805

Job	Run time
Style/format (ubuntu-latest, feat_os_unix)	23s
Style/spelling (ubuntu-latest, feat_os_unix)	2m 1s
Style/lint (ubuntu-latest, all, true)	1m 38s
Style/lint (macos-latest, feat_os_macos)	1m 6s
Style/lint (windows-latest, feat_os_windows)	2m 20s
Style/Python	6s
Style/toml	18s
Pre-commit hooks	39s
	8m 31s

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