Enable API handler by default as described in issue #272

[G4brym]

Enable API handler by default, following the discussion in issue #272 (#272). The feature should ensure that ApiException (and its subclasses) are automatically handled, so developers do not need to implement a global error handler manually. Consider integrating the handler logic into OpenAPIRoute, such as a default implementation for handleApiException.

Reference for implementation and expected behavior: issue #272.

[AndrewDNelson]

Just want to add on: As with the confusion found in issue #272, I too also found the docs to be misleading when it says: "When an ApiException is thrown within a Chanfana endpoint's handle method, Chanfana will automatically catch it and return an HTTP response with:" and "While Chanfana provides structured exception handling within endpoints, you might also want to implement global error handling for your application to catch unhandled exceptions or perform centralized error logging and reporting".

I interpreted that to mean the exception handling to be automatic while within the handle() method. Especially since ZodErrors are automatically handled already.