Upgrade to ESLint v9 flat config (#34324)

Co-authored-by: Nick Schonning <nschonni@gmail.com>

streaming/eslint.config.mjs

@@ -0,0 +1,45 @@
+// @ts-check
+
+import globals from 'globals';
+import tseslint from 'typescript-eslint';
+
+// eslint-disable-next-line import/no-relative-packages -- Must import from the root
+import { baseConfig } from '../eslint.config.mjs';
+
+export default tseslint.config([
+  baseConfig,
+  {
+    languageOptions: {
+      globals: globals.node,
+
+      parser: tseslint.parser,
+      ecmaVersion: 2021,
+      sourceType: 'module',
+    },
+
+    settings: {
+      'import/ignore': ['node_modules', '\\.(json)$'],
+      'import/resolver': {
+        typescript: {},
+      },
+    },
+
+    rules: {
+      // In the streaming server we need to delete some variables to ensure
+      // garbage collection takes place on the values referenced by those objects;
+      // The alternative is to declare the variable as nullable, but then we need
+      // to assert it's in existence before every use, which becomes much harder
+      // to maintain.
+      'no-delete-var': 'off',
+
+      'import/no-extraneous-dependencies': [
+        'error',
+        {
+          devDependencies: ['**/*.config.mjs'],
+        },
+      ],
+
+      'import/extensions': ['error', 'always'],
+    },
+  },
+]);