[AI-6470] Add EventBusOrchestrator to ddev (#22394)

* Add EventBusOrchestrator to ddev

* Fix formatting

* Add changelog

* Finalize threadpool executor implementation and property generic typing

* Improvements

* Small update on tests

* Addres comments about naming, queue injection and test setup for clarity

* Address comments in message pump finalization and error handling on task cancellations

Author: AAraKKe

ddev/changelog.d/22394.added

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+Add EventBusOrchestrator to ddev toolset

ddev/src/ddev/event_bus/__init__.py

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+# (C) Datadog, Inc. 2026-present
+# All rights reserved
+# Licensed under a 3-clause BSD style license (see LICENSE)

ddev/src/ddev/event_bus/exceptions.py

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+# (C) Datadog, Inc. 2026-present
+# All rights reserved
+# Licensed under a 3-clause BSD style license (see LICENSE)
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from .orchestrator import BaseMessage
+
+
+class ProcessorQueueError(Exception):
+    """
+    Exception raised when a processor queue is not initialized.
+    """
+
+    pass
+
+
+class MessageProcessingError(Exception):
+    """
+    Exception raised when a processor fails to process a message.
+    """
+
+    def __init__(self, processor_name: str, message: BaseMessage, original_exception: Exception):
+        self.processor_name = processor_name
+        self.message = message
+        self.original_exception = original_exception
+        super().__init__(
+            f"Error processing message by processor '{processor_name}'. "
+            f"Message: {message}. Original error: {original_exception}"
+        )
+
+
+class ProcessorSuccessHookError(MessageProcessingError):
+    """
+    Exception raised when the on_success hook of a processor fails.
+    """
+
+    def __init__(self, processor_name: str, message: BaseMessage, original_exception: Exception):
+        super(Exception, self).__init__(
+            f"Error in 'on_success' hook for processor '{processor_name}'. "
+            f"Message: {message}. "
+            f"Original error: {original_exception}"
+        )
+        self.processor_name = processor_name
+        self.message = message
+        self.original_exception = original_exception
+
+
+class FatalProcessingError(Exception):
+    """
+    Raised by hooks or processors to signal that the Orchestrator should
+    stop processing immediately and shutdown gracefully.
+    """
+
+    pass