refactor: clean up and refactor PR code

- Refactor duplicated video event listener boilerplate in wireVideoEvents()
  into onVideoEvent() helper (viewer.js: -57 lines)
- Fix 3 ESLint no-unused-vars warnings (bare catch instead of unused _e)
- Fix 1 additional no-unused-vars: unused 'data' param in MANIFEST_LOADED
- Remove dead 'Hls.cast' entry from playerRank map (no strategy produces it)
- Remove deprecated .eslintignore file (ESLint v9 uses flat config only)
- Add __tests__/ to ESLint ignores in flat config

Net: -20 lines (46 ins, 66 del). 83/83 tests pass, lint clean (0 warnings)

src/viewer/index.js

@@ -404,7 +404,6 @@ function dedupManifests(allManifests) {
     '__goon_plugin_data': 0,
     'content-script-intercept': 0,
     'video._goon_hls_manifest': 1,
-    'Hls.cast': 1,
     'inline-script': 99,
   };
   unique.sort((a, b) => {