Decouple some API in historybuf so that we can access more than just … #8941

Job	Run time
macOS Brew	3m 23s
Test ./dev.sh and benchmark	1m 39s
Linux (python=3.9 cc=gcc sanitize=0)	1m 57s
Bundle test (ubuntu-latest)	2m 12s
Linux (python=3.10 cc=gcc sanitize=1)	2m 27s
Bundle test (macos-latest)	2m 15s
Linux package	10m 51s
Linux (python=3.11 cc=clang sanitize=1)	2m 13s
	26m 57s

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