vici: Defer read/write error reporting after connection entry has been released

vici: Defer read/write error reporting after connection entry has been released

If a vici client registered for (control-)log events, but a vici read/write
operation fails, this may result in a deadlock. The attempt to write to the
bus results in a vici log message, which in turn tries to acquire the lock
for the entry currently held.

While a recursive lock could help as well for a single thread, there is still
a risk of inter-thread races if there is more than one thread listening for
events and/or having read/write errors.

We instead log to a local buffer, and write to the bus not before the connection
entry has been released. Additionally, we mark the connection entry as unusable
to avoid writing to the failed socket again, potentially triggering an error
loop.