Fix method naming and call in TurnstileVerifier

[JudahSan]

Summary

Renamed attempt_verification? to attempt_verification to accurately reflect
its behavior (network call with retries and logging, not a simple predicate).
Updated the verify method to call the corrected method.

Problem

The mismatch between the method definition (attempt_verification?) and its call
(attempt_verification) triggered a runtime error during user authentication:

NameError: undefined local variable or method `attempt_verification`
app/services/turnstile\_verifier.rb:30\:in `TurnstileVerifier#verify'
  app/controllers/users/sessions_controller.rb:18:in `Users::SessionsController#verify\_turnstile'

This caused signup/login requests to fail with a 500 Internal Server Error.

Fix

• Rename attempt_verification? → attempt_verification

Impact

• User signup/login with Turnstile verification now works as expected
• Prevents authentication flow from breaking due to undefined method errors