Simulator limitations

[GDYendell]

A collection of issues discovered when running against the simulator that may require it to be updated to match the real detector.

• [x] Some parameters have the wrong type causing the wrong PVs to be generated
• [x] Acquisition logic ignores ntrigger. It should run ntrigger subacquisitions of nimage frames. Currently it only does one regardless of the value of ntrigger.
• [x] Add special handling for subsystem keys that avoids nesting response within {"value": [keys]}. The response should just be [keys]
• [x] Return 404 when commands that don't take a value are given one

[GDYendell]

Will be resolved in https://github.com/DiamondLightSource/tickit-devices/pull/111