History of CasFs::readlink 1 change

In crates/flow-casfs/src/main.rs, lines 219–224 on f4dfd742b30df3764874975863da9d780d729d5c9fb543989c49ba1adc7c3189. 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 219,224:crates/flow-casfs/src/main.rs.