Serialize plan results to JSON compatible types earlier

When a plan returns a value that is serializable but contains a nested
value that is not (eg a list of an unserializable type), the check for
whether it could be serialized was too lenient and the unserializable
type would be stored only to fail later when it was sent to the message
bus.

Converting the result to a json compatible type (using mode='json')
earlier allows any issues with nested fields to be caught and handled
appropriately.

Author: tpoliaw

src/blueapi/worker/event.py

@@ -4,6 +4,7 @@
 
 from bluesky.run_engine import RunEngineStateMachine
 from pydantic import Field, PydanticSchemaGenerationError, TypeAdapter
+from pydantic_core import PydanticSerializationError
 from super_state_machine.extras import PropertyMachine, ProxyString
 
 from blueapi.utils import BlueapiBaseModel
@@ -73,8 +74,8 @@ class TaskResult(BlueapiBaseModel):
     def from_result(cls, result: Any) -> Self:
         type_str = type(result).__name__
         try:
-            value = TypeAdapter(type(result)).dump_python(result)
-        except PydanticSchemaGenerationError:
+            value = TypeAdapter(type(result)).dump_python(result, mode="json")
+        except (PydanticSchemaGenerationError, PydanticSerializationError):
             value = None
         return cls(result=value, type=type_str)