[NOT FOR MERGE] Add Blank Skip to Zipformer2

[ezerhouni]

I will double check that I am not missing something.

cc @csukuangfj

[yfyeung]

Thanks!

[ezerhouni]

@csukuangfj @danpovey If merging this PR is not very urgent and useful (>2 weeks), I can run it librispeech with all the changes needed (from review this PR) update Results.md

[danpovey]

We also need to see whether this might cause a problem for streaming systems, e.g. does it support streaming_forward().

[csukuangfj]

@csukuangfj @danpovey If merging this PR is not very urgent and useful (>2 weeks), I can run it librispeech with all the changes needed (from review this PR) update Results.md

That would be great. We have not used blank skipping with the latest zipformer.

[ezerhouni]

@danpovey It should work with streaming_forward @csukuangfj I will try to schedule that asap. In the meantime, any review would be welcome (so that I can test the reviewed code)

Thank you