op-node/rollup/derive: Investigate using a Peek/Discard io.Reader in BatchReader

[sebastianst]

The BatchReader might be improved to save one buffered reader instantiation by receiving a reader with Peek and Discard functions.

It should be checked if this is feasible in all places where the BatchReader is used, and in this case do the change.

Original Conversation:

          What if we took a peekable/discard reader instead of a generic reader here? Realistically the underlying type is a bytes.Buffer

Also, what if we passed the chainspec object to the batcher reader rather than flags like the limit + isFjord (edit: We need a to pass a "chain rules" object which contains these values for the pipeline origin).

Originally posted by @trianglesphere in #10358 (comment)