Camera layer fixes + stage scan speed restore

[bls337]

Stage scan

• fix stage scan speed restore, he "Max speed of X axis is small" prompt set the stage speed but not the value finish() restores, so the scan speed was written back at the end of every run and the prompt returned forever. 1.4 updates both,

Camera layer

• restore camera library switch for pseudo-overlap, 1.4 branches per camera library here with a default: error for unrecognised ones. Both engines had lost it (SCAPE collapsed it to if (!PVCAM), diSPIM dropped it entirely), so any non-PVCAM camera silently got the PCO exposure formula.
• read camera mode from settings, not camera readback, the engines asked the camera which trigger mode it was in, but that readback is lossy on PVCAM (pseudo-overlap reads back as edge trigger). 1.4 has no camera-mode getter at all, the settings are the only source. SCAPE already worked around this; diSPIM did not.
• remove redundant implements LightSheetCamera, subclasses re-declared what CameraBase already implements.
• make vendor camera methods abstract / add UnknownCamera, getResolution, getBinning, getReadoutTime, getResetTime, getRowReadoutTime and setBinning returned 0 or 0×0 on the base, so a camera class that omitted one inherited a plausible zero that fed straight into slice timing. They are now abstract. All five existing camera classes already implemented all six, so none needed changing.