Quic and Slic fixes

[bentoi]

This PR provides a number of fixes:

• it fixes the Quic multiplexed stream to no longer dispose the Quic stream when reads and writes are closed. Doing this is opens a can of worms. We're back to the previous behavior where the Quic stream is disposed when Input/Output are completed.
• it aligns the Slic ReadsClosed semantics with Quic, ReadsClosed is completed as soon as the last piece of data is returned from ReadAsync (instead of being completed when the data is singled consumed by the app with AdvanceTo)
• it simplifies the stream ReadsClosed and WritesClosed tasks to no longer raise exceptions.
• it updates some code in the icerpc protocol connection implementation to no longer dispose the dispatchCts or invocationCts from the unregister stream callback.

Protocol tests with Quic now work. It fixes #2287 but it doesn't fix #2300 or #2348.

[bernardnormier]

Can you open a proposal that describes what you've implemented here?

Keeping an async-disposable multiplexed stream where DisposeAsync:

• does nothing for Quic
• does not complete Input/Output with Slic

is not a correct API in my view.

[bentoi]

Can you open a proposal that describes what you've implemented here?

Opened #2381

[pepone]

Looks good, there are still a few references to DiposeAsync in SlicStream comments. There are also a few background tasks that do not handle non-IceRpcExceptions and will end up as UTE, I guess we can fix this in a separate PR for #2351