Enhance event processing by tracking failed events and updating statistics

[fadhilyori]

This pull request introduces several changes to the internal/app/app.go file to improve error handling and logging for failed events. The key changes include adding a failedCount field to the CompletedEvent struct, updating the processMessage method to return the count of failed events, and modifying the PrintStats method to include the total number of failed events in the log output.

Enhancements to error handling and logging:

• internal/app/app.go: Added failedCount field to the CompletedEvent struct to track the number of failed events.
• internal/app/app.go: Updated the App struct to include a total field to keep track of the total number of processed events.
• internal/app/app.go: Modified the PrintStats method to include failedEventsTotal in the log output and update the total field with the number of processed events.
• internal/app/app.go: Enhanced the EventLoop to log the number of failed events and update the CompletedEvent struct with failedCount.
• internal/app/app.go: Updated the processMessage method to return the count of failed events and handle errors accordingly. [1] [2] [3]