slice buffers in audioadapter and gap handling in whitener

related to this MR in sgn-ts: sgn-ts!42 (merged)

1. Whiten element

   1. Set adapter_config.skip_gaps = True, from which the _TSTransSink base class will produce gap buffers if there are any gaps in the segment to be processed
   2. If the whiten element sees that the preparedframe is a gap, it will first drain the output history, and produce gap buffers when it's empty
   3. plots
      1. FFT length 4 stride 1 sec
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      2. FFT length 4 stride 0.25 sec
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      3. FFT length 8 stride 1 sec
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      4. FFT length 8 stride 0.25 sec
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2. LLOIDCorrelate

   1. When concatenating data, only concatenate the union of segments from different time slices.