Implement decoding for codecv8 batches

[Thegaram]

TBA, pending on codec specification. https://www.notion.so/scrollzkp/codecv8-specification-2077792d22af80a7a6ede3d8e8608e77?source=copy_link

[Thegaram]

Currently most changes are dropped, but we'll still need to set codec version to v8 and maybe make some small changes, so keeping this open.

[greged93]

Any changes relevant to decoding? I couldn't find any