Phase 4b: dailyrun.FilerListFunc returns a bootstrap.ListFunc that
streams entries under <bucketsPath>/<bucket> by paginated SeaweedList.
Recurses into regular directories; .versions/ and .uploads/ are
skipped at this stage so they don't surface as raw children — the
sibling expansion (versioned NoncurrentDays state, MPU init dispatch)
lands in the next commit.
listAll and isVersionsDir are ported from scheduler/bootstrap.go's
same-named helpers. Phase 5 deletes the scheduler copies along with
the streaming path.
Tests pin: flat listing, recursion through nested directories,
.versions/ and .uploads/ skipped, kill-resume via the start path
contract, nil-client error, attribute propagation (mtime / size /
IsLatest default).