Make the routewatch tests pass on a loaded host (closes #213)

Five prefix handler tests gave HandleMessage two seconds to apply a full
batch of 25,000 prefixes. Under the race detector on a loaded host that
takes longer, so they failed although nothing waited. A test now waits up
to stepTimeout, 15 seconds, for each step it expects.

The slowest tests filled production limits: 500,000 paths in the peering
handler, and 30,000 table changes or 250,000 updates in the prefix handler.
The handlers' unexported constructors now take these limits, as they take
their timer interval, and those tests give small ones. This also fixes
#215.

The test helpers bound every wait, Stop included, so a test that hangs in
one fails with its own message.

Model: opus-5-5

TODO.md

@@ -35,6 +35,12 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: the tests of `internal/routewatch` no longer fail on a loaded
+  host. Five of them gave `HandleMessage` two seconds to apply a full prefix
+  batch, which under the race detector can take longer. A test now waits up to
+  15 seconds for each step it expects. The tests of the peering handler's path
+  limit and of the prefix handler's limits give the handler small limits, so the
+  package no longer runs past its 90-second limit (closes #213, #215)
 - 2026-10-27: the server works out the home page's cards every minute until it
   stops. It used to work them out only once, at startup: the end of the context
   that `Start` is given stopped the refreshes (closes #211)