io: Refactor out usage of Weak in the io handle

[LucioFranco]

Remove the use of Weak in the I/O Driver handle similar to how the timer does it. This will allow the IoHandle to store Arc<Inner> rather than require Weak::upgrade to access the inner timer.

The reason for Weak was to avoid cycles caused by wakers stored in the driver pointing to the runtime which points back to the driver. The cycle can be broken by making sure nobody can register a new io resources on (shutdown?) and by emptying the driver.

[hidva]

Hi, everyone, I have communicated with Lucio and I will try to solve this problem this week.