DRY refactor plus pinned-output regression tests and CI

[oetiker]

Summary

• Refactor the repeated patterns in zzclone into helper subs: transfer_cmd() (the send | mbuffer | receive pipeline existed 4×), snap_name() (5 scattered snapshot-name regexes in 3 spellings), read_lines() (4 hand-rolled pipe-open loops), list_snapshots() and get_guid(). The full-send branch now reuses the already-computed $dest_fileset instead of re-deriving the destination by string surgery (this also anchors the src-root substitution, fixing a latent quirk).
• Add t/regression.t: runs zzclone against a canned fake zfs/ssh/sudo world (t/shims) across 14 option combinations and compares stdout, stderr and exit code with pinned expected output (t/expected). The fake dataset tree covers incremental, full-send, up-to-date, no-snapshot, resume-token and guid-mismatch paths, in local, remote-source and remote-destination flavours. UPDATE_EXPECTED=1 prove t/ regenerates the expected files after an intentional output change.
• Add a GitHub Actions workflow running perl -c and prove t/ on pushes to main and on PRs.
• README: document the previously missing -R/--rollback, -c/--chain and -v/--verbose options and add a Testing section.

Verification

The generated output is byte-identical before and after the refactor: the pre-refactor script passes the exact same pinned test suite (all 28 tests) as the refactored one. No dependencies beyond core Perl; prove ships with it.

🤖 Generated with Claude Code