manual bump to gts 7, and necessary code nits (#7826)

Modifies the config file to the flat format described
[here](https://eslint.org/docs/latest/use/configure/migration-guide#start-using-flat-config-files).

Also, `.eslintrc.json` has been deprecated in eslint 9, [being replaced
by
`eslint.config.js`](https://eslint.org/docs/latest/use/migrate-to-9.0.0#-new-default-config-format-eslintconfigjs).
Opted to use CommonJS here because it's cleaner, matches up with the
[gts README example](https://github.com/google/gts#working-with-eslint)
and we shouldn't need to migrate for a while.

There are some stricter lint rules introduced by the Typescript updates:
```
@typescript-eslint/no-unused-expressions
@typescript-eslint/no-wrapper-object-types
```
that I also patched up in the code.

---------

Co-authored-by: Pavol Juhas <juhas@google.com>

Author: seunomonije

cirq-web/cirq_web/.eslintignore

@@ -0,0 +1,21 @@
+module.exports = [
+  ...require('gts'),
+  {
+    ignores: [
+      'build/',
+      '**/node_modules/',
+      '**/dist/',
+      'vitest.config.ts',
+      'vitest.setup.ts',
+      'vite.config.ts',
+      'vitest.e2e.config.ts',
+    ],
+  },
+  {
+    files: ['**/*.ts'],
+    rules: {
+      'n/no-unpublished-import': 'off',
+      'max-len': ['error', 100],
+    },
+  },
+];