fix(s2n-quic-transport): decrement handshake count for non-accepted finalized connections

[WesleyRosenblum]

Description of changes:

The count of currently handshaking connections in the connection container was not being decremented when a connnection moved from handshaking directly to finalizing. This change corrects this behavior.

Call-outs:

There is a brief moment between when update_interests() is called and finalize_done_connections() is called when the handshake_connections count is technically incorrect. This is because I decided to account for both handshaking connections and handshaking completed connections in the update_interests() method so I would not need to lock the connection multiple times. A connection that is handshaking and finalizing will decrement the handshake_connections count, but is not be removed from the connection map until finalize_done_connections is called. This meant I had to call finalize_done_connections() prior to ensure_counter_consistency(). I added some debug assertions in finalize_done_connections() to ensure the accounting is still correct.

Testing:

Updated the connection container fuzz test to trigger this scenario

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.