Add Tests for PR#1245

[codecov-ai]

This PR adds tests for #1245

Commits:

• Add comprehensive unit tests for api/gen_ai/math.py module

This commit adds unit tests for all functions and classes in the new math.py module,
including basic arithmetic functions, factorial, fibonacci, prime checking,
Calculator class, StringManipulator class, DataProcessor class, and utility functions.
Tests include both normal operation and edge cases.

• Restore payment failure test and add tests for error handling in StripeWebhookHandler

This commit:

1. Restores the test_customer_subscription_updated_payment_failed test
2. Adds test for the new default_event_handler functionality
3. Adds test for error handling in the post method

• Add tests for new StripeWebhookHandler methods

This commit adds unit tests for the new methods added to StripeWebhookHandler:

• payment_intent_payment_failed
• charge_refunded
• dispute_created
• invoice_updated
• account_updated
• default_event_handler
• simulate_delay
• revalidate_subscription

The tests verify the methods' behavior, error handling, and email notifications.

[seer-by-sentry]

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