feat: Add a base ClientTransport class, create a new JSONRPC and gRPC transport implementations, and introduce a new transport-independent Client implementation

Author: fjuma

client/pom.xml

@@ -20,17 +20,14 @@
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>a2a-java-sdk-common</artifactId>
-            <version>${project.version}</version>
         </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>a2a-java-sdk-spec</artifactId>
-            <version>${project.version}</version>
         </dependency>
         <dependency>
             <groupId>${project.groupId}</groupId>
             <artifactId>a2a-java-sdk-spec-grpc</artifactId>
-            <version>${project.version}</version>
         </dependency>
 
         <dependency>