feat: add unit tests for routing strategies and implement dynamic selector updates

Added comprehensive tests for `FillFirstSelector` and `RoundRobinSelector` to ensure proper behavior, including deterministic, cyclical, and concurrent scenarios. Introduced dynamic routing strategy updates in `service.go`, normalizing strategies and seamlessly switching between `fill-first` and `round-robin`. Updated `Manager` to support selector changes via the new `SetSelector` method.

sdk/cliproxy/auth/manager.go

@@ -135,6 +135,18 @@ func NewManager(store Store, selector Selector, hook Hook) *Manager {
 	}
 }
 
+func (m *Manager) SetSelector(selector Selector) {
+	if m == nil {
+		return
+	}
+	if selector == nil {
+		selector = &RoundRobinSelector{}
+	}
+	m.mu.Lock()
+	m.selector = selector
+	m.mu.Unlock()
+}
+
 // SetStore swaps the underlying persistence store.
 func (m *Manager) SetStore(store Store) {
 	m.mu.Lock()