History of Pool::keep 4 changes

In crates/flow/src/cache.rs, lines 230–265 on 069e16fba3bd50f76b63edc58b2edc7b876f018669946b92a7028687dc18a21e. Every change that wrote or deleted one of these lines, or deleted a line from between them. Exact, because each line keeps its identity across edits; edits elsewhere in the file are not here. Also: oxy log -L 230,265:crates/flow/src/cache.rs.