History of Pool::keep 4 changes

In crates/flow/src/cache.rs, lines 230–265 on 72e9cfca63b535d6cef20a3169d7305da8548271fbd7e51691f3f6974a20671a. 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.