### Motivation:
In some cases we can crash because of a precondition failure when the
write timeout fires and we aren't in the running state. This can happen
for example if the connection is closed whilst the write timer is
active.
### Modifications:
* Remove the precondition and instead take no action if the timeout
fires outside of the running state. Instead we take a new `Action`,
`.noAction` when the timer fires.
* Clear write timeouts upon request completion. When a request completes
we have no use for the idle write timer, we clear the read timer and we
should clear the write one too.
### Result:
Fewer crashes.
The supplied tests fails without these changes and passes with either of them.
Rick Newton-Rogers
f38c2fea86