feat: add stdout fallback in from_completed_process method

- Handle case when stdout_file is None by falling back to completed_process.stdout
- Create EntrypointOutput from captured stdout messages when no file provided
- Maintain backward compatibility for both file-based and memory-based stdout
- Addresses GitHub PR feedback from @aaronsteers

Co-Authored-By: AJ Steers <[email protected]>

Author: devin-ai-integration[bot]

airbyte_cdk/test/entrypoint_wrapper.py

@@ -301,7 +301,14 @@ def from_completed_process(
         stdout_file: Path | None = None,
     ) -> "EntrypointOutput":
         """Create EntrypointOutput from a completed subprocess with optional stdout file."""
-        instance = cls(message_file=stdout_file)
+        if stdout_file is not None:
+            instance = cls(message_file=stdout_file)
+        elif completed_process.stdout:
+            messages = completed_process.stdout.splitlines()
+            instance = cls(messages=messages)
+        else:
+            instance = cls()
+
         instance._completed_process = completed_process
         return instance