Show the progress rate over the last 5 seconds, and what a phase is doing after 10 seconds with no item done (closes #125)

The rate was the phase's average, so a burst after a long wait read as
over 1,000 files a second. It now covers the items completed over the
last 5 seconds, or since the line before off a terminal; the ETA still
comes from the average. Once no item has completed for 10 seconds, the
rate gives way to "stalled" and what the phase is doing, as "stalled
reading", kept whole with the phase, progress, elapsed time and ETA, so
only the bar gives way before them. report's read phase says
"read/write", as it writes the report while it reads. The tests set the
display's clock by hand.

Deviation: the stall words hold no time; with one, no words naming the
work fit beside the rest at 80 columns.
Judgement call: trees' group phase says "grouping".

Model: opus-5-5

TODO.md

@@ -29,6 +29,18 @@
 
 # Completed Steps
 
+- the rate a progress display shows covers the items completed over the last 5
+  seconds, or since the line before when stderr is not a terminal, so it falls
+  to 0 while nothing completes, and a burst after a wait no longer reads as a
+  steady rate of over 1,000 files a second; the ETA still comes from the phase's
+  average. Once no item has completed for 10 seconds, the word `stalled` and
+  what the phase is doing take the rate's place, as `stalled reading`, each
+  phase naming its own work where it is defined; `report`'s `read` says
+  `read/write`, as it writes the report while it reads. Those words are kept
+  whole with the phase, progress, elapsed time and ETA, so only the bar gives
+  way before them, and they fit on an 80-column terminal in an ordinary scan
+  (2026-10-16, https://git.eeqj.de/sneak/sfdupes/issues/125)
+
 - new subcommand `info` prints the database's details on stdout, one per line as
   a name, a tab and the value: its path and where it came from, the sizes of the
   database file and of its `-wal` file when there is one, when the database file