refactor: adopt POSITIONS constants and fix ESLint warnings

Replace hardcoded position strings with POSITIONS.* constants.
Prefix unused variables with _ to resolve no-unused-vars warnings.
Fix no-prototype-builtins where applicable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/nodeClass.js

@@ -223,7 +223,7 @@ class nodeClass {
    * Attach the node's input handler, routing control messages to the class.
    */
   _attachInputHandler() {
-    this.node.on('input', (msg, send, done) => {
+    this.node.on('input', (msg, send, _done) => {
      /* Update to complete event based node by putting the tick function after an input event */
       const m = this.source;
       switch(msg.topic) {