This PR adds tests for #1245

Commits:

• Add comprehensive unit tests for the new math module in api/gen_ai

This commit adds extensive test coverage for all functions and classes in the api/gen_ai/math.py module including:

• Basic arithmetic functions
• Factorial and Fibonacci calculations
• Prime number detection
• Calculator class with memory functionality
• String manipulation utilities
• Statistical data processing
• Date parsing and safe data access utilities
• Dictionary merging functionality

Tests cover both normal operation and edge cases.

• Remove test for payment failure detection in customer_subscription_updated

This commit removes the test case for the payment failure detection logic that
was deleted from the customer_subscription_updated method. Since the implementation
no longer checks for pending_update as an indication of payment failure, the
corresponding test is no longer relevant.

• Add test to verify removal of payment failure detection logic

This commit adds a new test file specifically focused on the StripeWebhookHandler
to verify that the customer_subscription_updated method no longer considers
the presence of a pending_update field as an indication of payment failure.
The test ensures that owners' delinquent status is not updated even when a
subscription with pending_update is processed.