History of unpack 2 changes

In crates/flow/src/checkpoint.rs, lines 109–164 on 8a4f5174526a58cc31b020871e52b8ff84f7fc3f5a2b544ff7b65db27c997a89. 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 109,164:crates/flow/src/checkpoint.rs.