do not chunk when performing beamforming

[popcornell]

as pointed out by @kamo-naoyuki, there are currently problems when doing the beamforming due to the fact that the a-posteriori SNR reference channel selection is performed for each freq chunk independently (and this requires a reduction over the freq axis).
The easy fix is to avoid to chunk frequencies when doing the beamfoming. Hopefully it is still ok and will not lead to OOMs

[popcornell]

@kamo-naoyuki, did you had a chance to try ?
For me the results are the same as with the old code. But may it be because my GPUs are 40GB VRAM.

@desh2608 can you merge ? I confirmed this does not impact the results.

[desh2608]

I am concerned that this may cause GPU OOMs when the segment is long and/or we are using a large number of channels. It may be better to have a CLI option to set bf chunking on/off (turned on by default). Could you make this change?

[popcornell]

Yes but then we need to also disable the channel selection inside the beamformer when the option is disabled.

Or IDK beamforming part needs to be changed quite a lot to accomodate for chunking but only before the channel.selection