Have an error if a device composite is not found in the blueapi context

[noemifrisina]

When injecting a device composite instead of a single device, if the composite has not been added to the module and not discoverable by blueapi, the only error that will show up on the blueapi logs is a PydanticInvalidForJsonSchema pointing to the first device in the composite, eg

raise self._value
pydantic.errors.PydanticInvalidForJsonSchema: Cannot generate a JsonSchema for core_schema.IsInstanceSchema (<class 'dodal.devices.beamlines.i19.diffractometer.FourCircleDiffractometer'>)

This is a bit confusing because it doesn't really give any information about where the error might be - in particular when the device otherwise connects and is used in other plans.

Related to #1525 . Run into this while testing on I19 and couldn't figure out what was missing until I took a look at the planFunctions module used in hyperion.

[tpoliaw]

I'm not sure how this can be related to not having the composite type imported. Without the import blueapi will fail to import the module with eg NameError: name 'DemoComposite' is not defined.

One way I could see this error being raised is if the composite doesn't have allow_arbitrary_types=True in its config. At that point, any field that wasn't serialisable (most devices) would cause a "Cannot create JsonSchema` error.

Do you have an example of the plan module that was causing the problem?