fix: support valid JSON value in tool structured content output (#551)

- Change CallToolResult.structuredContent type from Map<String,Object> to Object
  to support both objects and arrays
- Update JsonSchemaValidator to validate any Object type, not just Maps
- Add test cases for array-type structured output validation
- Fix type casting in existing tests to handle the more generic Object type
- Deprecate CallToolResult constructors in favor of builder pattern
- Update server implementations to use CallToolResult builder

This allows tools to return arrays as structured content, not just objects,
which is required by the MCP specification for tools with array-type output schemas.

It is realated to MPC spec fix: https://github.com/modelcontextprotocol/modelcontextprotocol/issues/834



Fixes #550

BREAKING CHANGE!

Migration Guide:
----------------
1. If you're accessing CallToolResult.structuredContent():
   - Add explicit casting when you know it's a Map:
     Before: result.structuredContent().get("key")
     After:  ((Map<String,Object>) result.structuredContent()).get("key")

   - Or check the type first:
     if (result.structuredContent() instanceof Map) {
         Map<String,Object> map = (Map<String,Object>) result.structuredContent();
         // use map
     } else if (result.structuredContent() instanceof List) {
         List<?> list = (List<?>) result.structuredContent();
         // use list
     }

2. If you're creating CallToolResult instances:
   - Switch to using the builder pattern:
     Before: new CallToolResult(content, isError, structuredContent)
     After:  CallToolResult.builder()
               .content(content)
               .isError(isError)
               .structuredContent(structuredContent)
               .build()

3. If you're implementing JsonSchemaValidator:
   - Update your validate() method signature:
     Before: validate(Map<String,Object> schema, Map<String,Object> structuredContent)
     After:  validate(Map<String,Object> schema, Object structuredContent)

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>