Fix processor stream drain on bounded input

[tmosleyIII]

This pull request refactors the event processing logic in StandardProcessor to ensure output events are sent before handling input stream EOF, and adds a targeted test for this behavior. The main change is extracting the event processing and sending logic into a dedicated method, improving clarity and correctness when handling stream closure. Additionally, a new test verifies that outputs are sent before the processor returns on input EOF.

Event processing and stream handling improvements:

• Refactored the main event loop in StandardProcessor.Process by extracting the event processing and response sending logic into a new processAndSend method, ensuring that output events are always sent before the processor returns on input EOF. This change also improves error handling and code readability. [1] [2]
• Changed the handling of cases where there is no handler or an error occurs during event processing to return nil instead of exiting the goroutine, aligning with the new synchronous processing model.

Testing improvements:

• Added a new test TestProcessSendsOutputBeforeHandlingInputEOF in processor_test.go to verify that the processor sends output events before returning when the input stream ends. This test uses a fake stream and synchronizes handler execution to ensure correct behavior.

Other:

• Minor import statement reordering in processor.go for consistency.