Dodal unit tests attempt to connect to real devices, setup_context() unexpected behaviour

[rtuck99]

Whilst addressing

• Update MX beamlines to use new device factory #846

It was discovered that test_main_system::test_when_context_created_then_contains_expected_number_of_plans() was taking > 15s to complete

This is because it is actually creating and attempting to connect to real devices, instead of mocked ones. It fails but the error message is caught and no error message is printed as the relevant logger is not enabled, and the test passes.

Ostensibly this test should test that the plans are created as expected. for this to work setup_context() needs to support a mock parameter that can get passed to the beamline device factories. It used to but this was removed in DiamondLightSource/hyperion#1481 although this test never used it.

We should reinstate this override. The desired behaviour implied by 1481 does not happen (at least for ophyd_async) in any case since ophyd_async ensure_connected() always specifies the parameters to device.connect() explicitly which means that default implementation in device will always be overridden in production.

In addition, the wait_for_connection parameter is totally ignored as blueapi with_dodal_module() always invokes utils.connect_devices() unconditionally.

Acceptance Criteria

• setup_context() is rewritten so that it no longer promises to do things that it doesn't actually do
• unit tests pass without delay
• Talk to @DominicOram to find out what the actual use case was for having mock devices on the beamline - do they still exist?

[DominicOram]

The use case for having a mock device on the beamline is e.g.:

• A slit set fails in the middle of the night
• The slits are in the correct position, therefore there is no scientific reason that the beamline cannot run, but can no longer be moved/read
• We need a quick way of saying in the DAQ layer "replace this device with something that works enough to run"
• We have been doing this so far by replacing the default in the device instantiation to be fake_with_ophyd_sim: bool = True

The issue with the code in 1481 was that when you supplied setup_context(fake_with_ophyd_sim = False) it overrode the default in the device factory itself. A solution I guess could be that setup_context instead takes a param like override_and_mock_all, which if true will make everything a mock and if false falls back to the device default. We would then need to change this behaviour in https://github.com/DiamondLightSource/blueapi/blob/5d8524eeb5ad4de9a80a81c28afc33e17f656086/src/blueapi/core/context.py#L108