Remove extra lookups and memory allocations from tsort graph construction #10811

Job	Run time
Style/format (ubuntu-latest, feat_os_unix)	20s
Style/toml	19s
Style/lint (ubuntu-latest, all, true)	1m 22s
Style/lint (macos-latest, feat_os_macos)	50s
Style/lint (windows-latest, feat_os_windows)	1m 39s
Style/spelling (ubuntu-latest, feat_os_unix)	2m 55s
Style/Python	7s
Pre-commit hooks	47s
	8m 19s

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