* op-node: Cleanup channel definition

This moves some files around and then expands upon the Channel struct.
It is better built for adding frames + then reading data when it is
ready.

Some tests are still failing and I don't know why.

* ReadBatch in channel.go

* op-node: Fix channel.go + start of new interface

* fix lint

* op-node: Use simple channel decoding

* revert switch to reader

This was due to the difficulty in making the mocks work with the reader.

* fix lint

* fix bug around trying to use an empty chanel
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>