add health check for agent

- Updated command-line flag parsing.
- Moved GetAddress and GetNetwork to server.go

beszel/internal/agent/health.go

@@ -0,0 +1,19 @@
+package agent
+
+import (
+	"net"
+	"time"
+)
+
+// Health checks if the agent's server is running by attempting to connect to it.
+// It returns 0 if the server is running, 1 otherwise (as in exit codes).
+//
+// If an error occurs when attempting to connect to the server, it returns the error.
+func Health(addr string, network string) (int, error) {
+	conn, err := net.DialTimeout(network, addr, 4*time.Second)
+	if err != nil {
+		return 1, err
+	}
+	conn.Close()
+	return 0, nil
+}