History of Hub::checkpoint 1 change

In crates/flow/src/runner.rs, lines 253–266 on v0.5.1. 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 253,266:crates/flow/src/runner.rs.