Migrate ESLint to v9 with flat config and update dependencies (#594)

* Start ESLint v9 migration plan

Agent-Logs-Url: https://github.com/microsoft/vscode-hexeditor/sessions/f66f9eff-ec77-48af-b6ee-62752ebae19e

Co-authored-by: rzhao271 <7199958+rzhao271@users.noreply.github.com>

* Migrate ESLint to v9 with flat config and update dependencies

Agent-Logs-Url: https://github.com/microsoft/vscode-hexeditor/sessions/f66f9eff-ec77-48af-b6ee-62752ebae19e

Co-authored-by: rzhao271 <7199958+rzhao271@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rzhao271 <7199958+rzhao271@users.noreply.github.com>

Author: Copilot

.eslintignore

@@ -0,0 +1,32 @@
+import globals from "globals";
+import eslint from "@eslint/js";
+import tseslint from "typescript-eslint";
+
+export default tseslint.config(
+  {
+    ignores: ["node_modules/**", "**/*.d.ts", "**/*.js"],
+  },
+  eslint.configs.recommended,
+  tseslint.configs.recommended,
+  {
+    files: ["src/**/*.ts"],
+    languageOptions: {
+      globals: {
+        ...globals.node,
+        ...globals.browser,
+        ...globals.commonjs,
+        Atomics: "readonly",
+        SharedArrayBuffer: "readonly",
+      },
+    },
+    rules: {
+      "no-console": "off",
+      "no-var": "warn",
+      "no-case-declarations": "off",
+      "@typescript-eslint/no-unused-vars": ["warn", { argsIgnorePattern: "(^_)|(^h$)" }],
+      "@typescript-eslint/no-explicit-any": "off",
+      "@typescript-eslint/no-non-null-assertion": "off",
+      "object-curly-spacing": ["error", "always"],
+    },
+  },
+);