Make a timed batch write on every tick (closes #192)

The prefix, AS and peer handlers skipped a timed write unless one
interval had passed since the last write ended. The next tick came a
little less than one interval after that, so every other tick was
skipped. Each tick now writes. A full batch's write restarts the timer,
so the next timed write comes one interval after that write began.
Comparing clock readings would not do: two ticks one interval apart can
read a hair under it. flushBatch no longer reports whether it wrote a
batch, since nothing reads that. A new test runs the loop on a fake
clock and fails on the old code.

Model: opus-5-5

TODO.md

@@ -33,6 +33,10 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: the prefix, AS and peer handlers make a timed write on every tick
+  of their timers, every 1, 2 and 2 seconds. They used to skip every other tick.
+  A full batch's write restarts the timer, so the next timed write comes one
+  interval after that write began (closes #192)
 - 2026-10-27: once the stop deadline has passed, the AS, peer and peering
   handlers start no write either. A full batch or a tick of the timer that
   waited while a write ran past the deadline could still start one. The flush