refactor(api): address review feedback on int64_as_string PR

Three small adjustments per review on PR #6699:

- GetTransactionCountByBlockNumServlet: add trailing newline at end of
  file to satisfy checkstyle.
- Util.getInt64AsString: align control flow with the existing
  Util.getVisible (single-return via local boolean, Boolean.valueOf
  instead of Boolean.parseBoolean). Functionally identical -- both
  return true only when the parameter value is "true" (case-insensitive).
- Util.INT64_AS_STRING -> Util.INT64_AS_STRING_PARAM: rename the public
  parameter-name constant to avoid potential confusion with the unrelated
  private ThreadLocal field of the same simple name in JsonFormat.
  The user-facing query parameter remains "int64_as_string" -- only the
  Java identifier changes.

Author: waynercheung

framework/src/main/java/org/tron/core/services/http/GetTransactionCountByBlockNumServlet.java

@@ -45,4 +45,4 @@ private void fillResponse(long num, HttpServletResponse response) throws IOExcep
         : "{\"count\": " + count + "}";
     response.getWriter().println(out);
   }
-}
+}

framework/src/main/java/org/tron/core/services/http/Util.java

@@ -66,7 +66,7 @@ public class Util {
 
   public static final String PERMISSION_ID = "Permission_id";
   public static final String VISIBLE = "visible";
-  public static final String INT64_AS_STRING = "int64_as_string";
+  public static final String INT64_AS_STRING_PARAM = "int64_as_string";
   public static final String TRANSACTION = "transaction";
   public static final String TRANSACTION_EXTENSION = "transactionExtension";
   public static final String VALUE = "value";
@@ -355,10 +355,11 @@ public static boolean existVisible(final HttpServletRequest request) {
    * downstream servlets.
    */
   public static boolean getInt64AsString(final HttpServletRequest request) {
-    if (StringUtil.isNotBlank(request.getParameter(INT64_AS_STRING))) {
-      return Boolean.parseBoolean(request.getParameter(INT64_AS_STRING));
+    boolean int64AsString = false;
+    if (StringUtil.isNotBlank(request.getParameter(INT64_AS_STRING_PARAM))) {
+      int64AsString = Boolean.valueOf(request.getParameter(INT64_AS_STRING_PARAM));
     }
-    return false;
+    return int64AsString;
   }
 
   public static boolean getVisiblePost(final String input) {