Get rif of platform endcoding warning

Author: kabir

pom.xml

@@ -14,6 +14,7 @@
     <description>Java SDK for the Agent2Agent Protocol (A2A)</description>
 
     <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven-compiler-plugin.version>3.11.0</maven-compiler-plugin.version>
         <maven-surefire-plugin.version>3.1.2</maven-surefire-plugin.version>
         <jackson.version>2.17.0</jackson.version>