AWG 5014c warn about software sequencer

Warn when using elements shorter than 250 points that software sequencing mode is used which has several limitations including not being able to jump and trigger on elements in the middle of the sequence. This happens silently and is first revealed when trying to turn on the channel. Furthermore,
remote activating the channel with `awg.ch1_state(1)` fails silently

See Sequencer Mode in the awg5k7.chm help file

Note: For subsequences, only the software sequencer mode is used.

Item | Hardware Sequencer Mode | Software Sequencer Mode
-- | -- | --
Minimum Waveform Length
AWG7000 Series | 960 points (Interleave On: 1920 points) | No limitations
AWG5000 Series | 250 points | No limitations
Waveform Length Granularity
AWG7000B/AWG7000C Series | 4 points (Interleave On: 8 points) | No limitations
AWG7000 Series | 64 points (Interleave On: 128 points) | No limitations
AWG5000 Series | 1 point | No limitations
Wait Trigger | No limitations | First element only
Go To | No limitations | Last element only
Event Jump To | No limitations | Unable to use
Command Jump | No limitations | Unable to use
Infinite Repeat | No limitations | Last element only
Restrictions of Waveform Memory | None | Software sequencer uses more waveform memory than hardware sequencer. Expand waveform data into the least common multiple of the waveform length and the granularity to overcome the restriction of waveform length granularity. Repeat is implemented by repeating the waveform data in the hardware waveform memory.

Start by tracing the AWG5014c channel activation path, including the awg.ch1_state(1) entry point, and inspect how software sequencer mode is selected for short elements and subsequences. The work is done when using elements shorter than 250 points produces a clear warning about software-sequencer limitations instead of failing silently.

Written by the indexing model from the issue text.