Override ToString() methods instead of using new keyword

Updated three ToString() methods in SIPSorcery.SIP (SIPHeader.cs) to use the override keyword, ensuring proper method overriding and improved polymorphic behavior.

Author: paulomorgado

src/SIPSorcery/core/SIP/SIPHeader.cs

@@ -355,7 +355,7 @@ public static SIPViaHeader[] ParseSIPViaHeader(string viaHeaderStr)
             }
         }
 
-        public new string ToString()
+        public override string ToString()
         {
             return $"{SIPHeaders.SIP_HEADER_VIA}: {this.Version}/{this.Transport.ToString().ToUpper()} {ContactAddress}{((ViaParameters != null && ViaParameters.Count > 0) ? ViaParameters.ToString() : null)}";
         }
@@ -1191,7 +1191,7 @@ public void ReplaceRoute(string origSocket, string replacementSocket)
             }
         }
 
-        public new string ToString()
+        public override string ToString()
         {
             if (m_sipRoutes != null && m_sipRoutes.Count > 0)
             {
@@ -1311,7 +1311,7 @@ public void PushViaHeader(SIPViaHeader viaHeader)
             m_viaHeaders.Insert(0, viaHeader);
         }
 
-        public new string ToString()
+        public override string ToString()
         {
             if (m_viaHeaders != null && m_viaHeaders.Count > 0)
             {