refactor: change logger to final static

Author: DumiJDev

jlama-core/src/main/java/com/github/tjake/jlama/model/PromptBuilder.java

@@ -19,7 +19,7 @@ public class PromptBuilder {
   private final List<ToolCall> toolCalls = new ArrayList<>();
   private final List<ToolResult> toolResults = new ArrayList<>();
   private boolean isGenerational = false;
-  private final Logger logger = LoggerFactory.getLogger(PromptBuilder.class);
+  private static final Logger logger = LoggerFactory.getLogger(PromptBuilder.class);
 
   PromptBuilder(AbstractModel model) {
     this.model = model;