[io] Remember if uring failed in ReadV
[io] Remember if uring failed in ReadV

If uring fails for any reason, stop trying to use it and instead
fall back to blocking I/O for the rest of that thread's execution.
A thread_local bool was used instead of static to avoid UB in case
ReadV is called from separate threads. This means the warning will
print once for each thread failure.

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root