stats: generalize stat tracking loan extensions to track all transitions #1301

Job	Run time
Tests (acquisition, 3.9, pypi, postgresql14, opensearch2)	2m 31s
Tests (document_requests, 3.9, pypi, postgresql14, opensearch2)	3m 1s
Tests (circulation, 3.9, pypi, postgresql14, opensearch2)	8m 50s
Tests (ils, 3.9, pypi, postgresql14, opensearch2)	16m 12s
Tests (ill, 3.9, pypi, postgresql14, opensearch2)	4m 7s
	34m 41s

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