Fix for initialization in non-osgi environment case

Author: scottslewis

mcp-core/src/main/java/io/modelcontextprotocol/json/internal/DefaultMcpJson.java

@@ -26,6 +26,9 @@ void unsetMcpJsonMapperSupplier(McpJsonMapperSupplier supplier) {
 	}
 
 	public synchronized static McpJsonMapper getDefaultMcpJsonMapper() {
+		if (mcpMapperServiceLoader == null) {
+			new DefaultMcpJson();
+		}
 		return mcpMapperServiceLoader.getDefault();
 	}
 
@@ -38,6 +41,9 @@ void unsetJsonSchemaValidatorSupplier(JsonSchemaValidatorSupplier supplier) {
 	}
 
 	public synchronized static JsonSchemaValidator getDefaultJsonSchemaValidator() {
+		if (mcpValidatorServiceLoader == null) {
+			new DefaultMcpJson();
+		}
 		return mcpValidatorServiceLoader.getDefault();
 	}