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/specificClass.js

@@ -381,7 +381,7 @@ class Measurement {
     const lowPass = this.lowPassFilter(arr); // Apply low-pass filter
     const highPass = this.highPassFilter(arr); // Apply high-pass filter
   
-    return arr.map((val, idx) => lowPass + highPass - val).pop(); // Combine the filters
+    return arr.map((val, _idx) => lowPass + highPass - val).pop(); // Combine the filters
   }
   
   weightedMovingAverage(arr) {
@@ -558,7 +558,7 @@ const configuration = {
     enabled: true,
   },
   functionality: {
-    positionVsParent: "upstream"
+    positionVsParent: POSITIONS.UPSTREAM
   }
 };