Fix local optimization stats file path structure

Use a nested `filters/{filterId}/stats.json` path

A flat `{filterId}_stats.json` file is my typo

Author: mu-hun

src/main/optimization.js

@@ -59,7 +59,15 @@ export const getFilterOptimizationConfig = (filterId) => {
     let optimizationConfig = null;
     if (optimizationEnabled && filterOptimizationPercent) {
         const content = localOptimizationConfigDir
-            ? fs.readFileSync(path.join(localOptimizationConfigDir, `${filterId}_stats.json`), 'utf-8')
+            ? fs.readFileSync(
+                path.join(
+                    localOptimizationConfigDir,
+                    'filters',
+                    filterId.toString(),
+                    'stats.json',
+                ),
+                'utf-8',
+            )
             : downloadOptimizationStats(filterId);
 
         optimizationConfig = JSON.parse(content);