drainSlack stood for three things: the deadline given to a drain that
should finish early, the watchdog on a drain that should time out, and
the wait for a delivery to reach the test server. It is now three
constants, each commented with what it bounds and why it is 2s; no
value changed. The idle-drain failure printed that deadline instead of
idleDrainBound, the bound it checks. The cancelled-context test now
also requires the drain to return within idleDrainBound and to log its
debug line, so a drain that logs nothing no longer passes;
newLoggingService records debug level for this.
Model: opus-5-5
sneak