ref(uptime): Move subscription limit check to validator

[evanpurkhiser]

Move uptime subscription limit checking from exception handling in
create() to validator validation method. This ensures limits are checked
during validation phase when creating new uptime monitors, providing
consistent error responses and cleaner code.

Follows the same pattern as cron monitors for consistency.

[seer-by-sentry]

Potential bug: The create method no longer handles the MaxManualUptimeSubscriptionsReached exception, which can be raised during a race condition, causing a 500 error instead of a validation error.

• Description: The create method in UptimeMonitorValidator no longer handles the MaxManualUptimeSubscriptionsReached exception. This exception can be raised by check_uptime_subscription_limit, which is called within the creation logic. While a limit check was added to the validate method, a race condition can occur where concurrent requests cause the subscription limit to be exceeded between the validation and creation steps. Because the try...except block was removed from the create method, this race condition will lead to an unhandled exception, resulting in a 500 Internal Server Error instead of the expected 400 Bad Request with a validation error.

• Suggested fix: Wrap the call to super().create() within the create method in a try...except MaxManualUptimeSubscriptionsReached block. In the except block, raise a ValidationError to ensure subscription limit errors are handled gracefully as 400 responses, preventing 500 errors from race conditions.
  _{severity: 0.65, confidence: 0.98}

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Branches    24033     24033              
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- Hits       310199    310194       -5     
- Misses      71723     71732       +9     
  Partials      328       328