Reflectomtry: On set point of motor does not update produce a warning

As an instrument scientist I would like a warning to appear in the log if the setpoint of the motor can not be set for some reason to explain. Currently the rbv and set point would show as not matching but no explanation would be offered.

### Acceptance Criteria

- When set point is not accepted by the axis and error is written to the error log

### Notes

Not required for POLREF but a nice to have

Start by tracing the motor axis setpoint handling and the path that writes to the error log. Reproduce a case where the axis rejects the setpoint, then confirm that the log records an explanatory error when the readback value and setpoint do not match.

Scritto dal modello di indicizzazione a partire dal testo della issue.