implementing a simple graph hash to correct for a buggy `hash` / `==`… #1052

Job	Run time
Documentation	1m 56s
Julia 1.10 - windows-latest - x64 - push	9m 39s
Julia 1 - macos-latest - x64 - push	22m 20s
Julia 1.10 - ubuntu-latest - x64 - push	8m 17s
Julia pre - windows-latest - x64 - push	1m 11s
Julia 1 - ubuntu-latest - x64 - push	12m 50s
Julia 1 - windows-latest - x64 - push	16m 11s
Julia pre - macos-latest - x64 - push	1m 36s
Julia 1.10 - macos-latest - x64 - push	9m 15s
Julia pre - ubuntu-latest - x64 - push	41s
	1h 23m 56s

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