chore: move to Eslint flat config

Make the big move to Eslint flat config format. The outcome of Eslint
still should be the same, but some things has changed:
- `eslint-plugin-github` is dropped, flat configs have been out for a
while and most eslint plugins support it, but for no reason and no
activity in sight this plugin is likely not going to support flat config
for a while and to avoid other plugins not being able to update (as they
are requiring flat configs) drop the github rules.
- Nested configs don't work properly and are unified into the root
eslint config, this unification did cause some conflicts and thats why
the `import-x` is in a seperate 'group' to exclude targeting Vue files.
- The `eslint-plugin-i` is deprecated and `esplint-plugin-import-x` is
its succesor which has better support for flat configs, the same rules
are still applied.

The majority of the flat config was generated by
`@eslint/migrate-config` tool.

package.json

@@ -69,10 +69,9 @@
     "@vitest/coverage-v8": "2.1.3",
     "@vitest/eslint-plugin": "1.1.7",
     "@vue/test-utils": "2.4.6",
-    "eslint": "8.57.1",
+    "eslint": "9.13.0",
     "eslint-plugin-array-func": "4.0.0",
-    "eslint-plugin-github": "5.0.2",
-    "eslint-plugin-i": "2.29.1",
+    "eslint-plugin-import-x": "4.3.1",
     "eslint-plugin-no-jquery": "3.0.2",
     "eslint-plugin-no-use-extend-native": "0.5.0",
     "eslint-plugin-playwright": "1.6.2",
@@ -83,6 +82,7 @@
     "eslint-plugin-vue": "9.28.0",
     "eslint-plugin-vue-scoped-css": "2.8.1",
     "eslint-plugin-wc": "2.2.0",
+    "globals": "15.11.0",
     "happy-dom": "15.7.4",
     "license-checker-rseidelsohn": "4.4.2",
     "markdownlint-cli": "0.42.0",