Webclaw's default -t timeout is 30s; slow sites previously sat
silently with no feedback. Now during a fetch, every 10s of elapsed
time webclaw writes one line to stderr:
# webclaw: still fetching <URL> (Ns)
Fetches completing in under 10s emit nothing (the timer never fires).
Stdout output is untouched - pure feedback signal on stderr.
No timeout change. No new flags. Default behavior is augmented at
stderr only.
Implemented via tokio::select! between the fetch future and a
tokio::time::interval. Latency cost: a single tokio task spawn
and a 10s tick - microseconds on the fast path.
10 new tests in webclaw-fetch::progress::tests (none ignored; the
slow-future test uses a 50ms test interval to keep cargo test fast).
Workspace total 710 -> 720.
(cherry picked from commit 06f065cb08)
