feat: add verification flow helpers and integrate into background script

- Introduced a new module `verification-flow.js` containing verification flow helpers.
- Updated `background.js` to import and utilize the new verification flow helpers.
- Refactored existing verification-related functions to leverage the new helpers for improved code organization and maintainability.
- Added tests for the verification flow module to ensure proper integration and functionality.

tests/background-verification-flow-module.test.js

@@ -0,0 +1,17 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+
+test('background imports verification flow module', () => {
+  const source = fs.readFileSync('background.js', 'utf8');
+  assert.match(source, /background\/verification-flow\.js/);
+});
+
+test('verification flow module exposes a factory', () => {
+  const source = fs.readFileSync('background/verification-flow.js', 'utf8');
+  const globalScope = {};
+
+  const api = new Function('self', `${source}; return self.MultiPageBackgroundVerificationFlow;`)(globalScope);
+
+  assert.equal(typeof api?.createVerificationFlowHelpers, 'function');
+});