DS-4027: Reconnection Counter Underflow Fix

[andrejrakic]

Description

This PR fixes the Reconnection Counter Underflow issue and adds another unit test to confirm the fix.

What was the issue

Step	Code path	active_connections
Server sends Close frame	Message::Close arm → fetch_sub(1)	-1
Stream drains, yields None	None arm → fetch_sub(1)	-1 again ← bug
Reconnect succeeds	try_to_reconnect → fetch_add(1)	+1
Net per cycle		-1

Per WebSocket RFC 6455, after a Close frame the stream always yields None — the None arm is the definitive end-of-stream signal. The Message::Close arm should not decrement; removing that call makes each graceful close/reconnect cycle net-zero. Without the fix, repeated cycles underflow the AtomicUsize counter to usize::MAX, causing full reconnects to be misclassified as partial.