Fix tool result processing to accept any Map structure

Previously, Claude model only processed tool results if they
contained a 'result' key, ignoring other valid responses.
Now serializes the entire response Map to JSON.

Fixes #566

Author: stevearmstrong-dev

core/src/main/java/com/google/adk/models/Claude.java

@@ -170,9 +170,15 @@ private ContentBlockParam partToAnthropicMessageBlock(Part part) {
               .build());
     } else if (part.functionResponse().isPresent()) {
       String content = "";
-      if (part.functionResponse().get().response().isPresent()
-          && part.functionResponse().get().response().get().getOrDefault("result", null) != null) {
-        content = part.functionResponse().get().response().get().get("result").toString();
+      if (part.functionResponse().get().response().isPresent()) {
+        try {
+          ObjectMapper objectMapper = new ObjectMapper();
+          objectMapper.registerModule(new Jdk8Module());
+          content = objectMapper.writeValueAsString(part.functionResponse().get().response().get());
+        } catch (Exception e) {
+          logger.error("Failed to serialize tool response", e);
+          content = part.functionResponse().get().response().get().toString();
+        }
       }
       return ContentBlockParam.ofToolResult(
           ToolResultBlockParam.builder()