When a (1) capped channel has more than one consumer, one of them will
effectively remain blocking as the other consumes the message from
the channel. Closing the channel unblocks any/all consumers.

Here we also unpublish previously public ModuleOperation.Done()
to further prevent deadlocks in the future, i.e. effectively
to prevent any place that schedules tasks to wait.

The only reason we keep the channel there for now is to make testing
*within the package* easier.

Previously we would (mistakenly) not parse module in walker,
only when it's opened (as part of didOpen or didChange).

This fixes that to help publish diagnostics from all modules
at startup time.