[client] Supress ICE signaling (#5820)

* [client] Suppress ICE signaling and periodic offers in force-relay mode

When NB_FORCE_RELAY is enabled, skip WorkerICE creation entirely,
suppress ICE credentials in offer/answer messages, disable the
periodic ICE candidate monitor, and fix isConnectedOnAllWay to
only check relay status so the guard stops sending unnecessary offers.

* [client] Dynamically suppress ICE based on remote peer's offer credentials

Track whether the remote peer includes ICE credentials in its
offers/answers. When remote stops sending ICE credentials, skip
ICE listener dispatch, suppress ICE credentials in responses, and
exclude ICE from the guard connectivity check. When remote resumes
sending ICE credentials, re-enable all ICE behavior.

* [client] Fix nil SessionID panic and force ICE teardown on relay-only transition

Fix nil pointer dereference in signalOfferAnswer when SessionID is nil
(relay-only offers). Close stale ICE agent immediately when remote peer
stops sending ICE credentials to avoid traffic black-hole during the
ICE disconnect timeout.

* [client] Add relay-only fallback check when ICE is unavailable

Ensure the relay connection is supported with the peer when ICE is disabled to prevent connectivity issues.

* [client] Add tri-state connection status to guard for smarter ICE retry (#5828)

* [client] Add tri-state connection status to guard for smarter ICE retry

Refactor isConnectedOnAllWay to return a ConnStatus enum (Connected,
Disconnected, PartiallyConnected) instead of a boolean. When relay is
up but ICE is not (PartiallyConnected), limit ICE offers to 3 retries
with exponential backoff then fall back to hourly attempts, reducing
unnecessary signaling traffic. Fully disconnected peers continue to
retry aggressively. External events (relay/ICE disconnect, signal/relay
reconnect) reset retry state to give ICE a fresh chance.

* [client] Clarify guard ICE retry state and trace log trigger

Split iceRetryState.attempt into shouldRetry (pure predicate) and
enterHourlyMode (explicit state transition) so the caller in
reconnectLoopWithRetry reads top-to-bottom. Restore the original
trace-log behavior in isConnectedOnAllWay so it only logs on full
disconnection, not on the new PartiallyConnected state.

* [client] Extract pure evalConnStatus and add unit tests

Split isConnectedOnAllWay into a thin method that snapshots state and
a pure evalConnStatus helper that takes a connStatusInputs struct, so
the tri-state decision logic can be exercised without constructing
full Worker or Handshaker objects. Add table-driven tests covering
force-relay, ICE-unavailable and fully-available code paths, plus
unit tests for iceRetryState budget/hourly transitions and reset.

* [client] Improve grammar in logs and refactor ICE credential checks

client/internal/peer/guard/sr_watcher.go

@@ -39,7 +39,7 @@ func NewSRWatcher(signalClient chNotifier, relayManager chNotifier, iFaceDiscove
 	return srw
 }
 
-func (w *SRWatcher) Start() {
+func (w *SRWatcher) Start(disableICEMonitor bool) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
@@ -50,8 +50,10 @@ func (w *SRWatcher) Start() {
 	ctx, cancel := context.WithCancel(context.Background())
 	w.cancelIceMonitor = cancel
 
-	iceMonitor := NewICEMonitor(w.iFaceDiscover, w.iceConfig, GetICEMonitorPeriod())
-	go iceMonitor.Start(ctx, w.onICEChanged)
+	if !disableICEMonitor {
+		iceMonitor := NewICEMonitor(w.iFaceDiscover, w.iceConfig, GetICEMonitorPeriod())
+		go iceMonitor.Start(ctx, w.onICEChanged)
+	}
 	w.signalClient.SetOnReconnectedListener(w.onReconnected)
 	w.relayManager.SetOnReconnectedListener(w.onReconnected)