History of Pool::keep 3 changes

In crates/flow/src/cache.rs, lines 207–241 on v0.2.0. 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 207,241:crates/flow/src/cache.rs.