test(fc-commands): cover accel-cal cancel and SCALED_IMU helpers

[iacker]

Following up on the RCCalibrationDataModel test suite, this adds hardware-free tests for three FlightControllerCommands methods added on the RC_Calibration branch (#1816) that currently have zero coverage:

Method	Tests
cancel_accel_calibration	all-zero PREFLIGHT_CALIBRATION abort command, vehicle-position reset, no-connection guard, send-exception handling
poll_scaled_imu	(xacc, yacc, zacc) float triple, no-message → None, no-connection → None, exception swallowed → None
request_scaled_imu_messages	ACK success path, requested interval forwarded to the command, no-connection guard

Why

#1816 is flagged as WIP that "needs a lot more testing". These three backend methods are pure command/telemetry logic, so they can be fully exercised with the existing mock_connected_master fixture — no flight controller or SITL needed. This locks in their behaviour (especially the graceful-failure paths) while the RC calibration feature keeps evolving.

Validation

• 11 new tests, all green
• Full test_backend_flightcontroller_commands.py suite: 63 passed
• ruff check clean on the modified file
• Uses only the shared mock_connected_master fixture; no new fixtures or dependencies

Based on RC_Calibration so it merges cleanly alongside the WIP. Happy to rebase if the branch moves.

/kind cleanup

[iacker]

Heads-up on the red CI: none of the failures come from this PR. All failing tests are in the frontend tkinter files that already exist on the RC_Calibration base branch (test_frontend_tkinter_accelerometer_calibration.py, test/unit_frontend_tkinter_compass_calibration.py) — e.g. AttributeError: 'CompassCalibrationPopup' object has no attribute 'root' and the pyright Toplevel | Tk errors in frontend_tkinter_calibration_popup_base.py. Those are pre-existing on #1816.

My change only appends to tests/test_backend_flightcontroller_commands.py; that file passes clean:

tests/test_backend_flightcontroller_commands.py .... 63 passed
ruff check: All checks passed

Once the WIP frontend on RC_Calibration is fixed, this branch should go green with no changes on my side. Happy to rebase whenever.

[amilcarlucas]

Yes, I did refactor some files and that broke some of the tests. I`ll fix that.

Thanks for adding these tests.