Remove einsum in logit_attrs in ActivationCache #1783

Job	Run time
Code Checks	6m 33s
Compatibility Checks (3.9)	4m 31s
Notebook Checks (ARENA_Content)	1m 41s
Compatibility Checks (3.10)	3m 46s
Notebook Checks (Colab_Compatibility)	1m 9s
Notebook Checks (BERT)	1m 18s
Notebook Checks (Exploratory_Analysis_Demo)	5m 47s
Notebook Checks (Interactive_Neuroscope)	1m 30s
Notebook Checks (Main_Demo)	1m 49s
Notebook Checks (Othello_GPT)	1m 12s
Notebook Checks (Patchscopes_Generation_Demo)	6m 39s
Build Docs	0s
Deploy Docs	0s
	35m 55s

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