Add thread-safe Add/Del methods and refactor client locking

- Add Add and Del methods to Client for dynamic host management.
- Add RWMutex to Client to protect the devices map.
- Add Transport to Config to allow mocking HTTP transport in tests.
- Add getDeviceByHost helper to centralize device lookup locking.
- Refactor GetAll* methods to snapshot host keys before iteration to avoid concurrent map read/write panic.
- Add tests for thread safety and Add/Del functionality.

pkg/edgeos/config.go

@@ -1,6 +1,9 @@
 package edgeos
 
-import "time"
+import (
+	"net/http"
+	"time"
+)
 
 // Config represents the configuration for an EdgeOS device.
 type Config struct {
@@ -10,4 +13,6 @@ type Config struct {
 	Username string
 	Password string
 	Timeout  time.Duration
+	// Transport allows customizing the http transport (useful for testing)
+	Transport http.RoundTripper
 }