chore(protocol/interop): Interop Test Coverage

[refcell]

Description

The kona-interop crate currently sits at ~86% test coverage with 65 lines of code missing test coverage. This ticket is to bring that test coverage up to 98%.

[emhane]

currently at 92%

what link should we embedded in the test coverage icon @refcell ?

[emhane]

this one probs https://app.codecov.io/github/op-rs/kona/tree/main/crates%2Fprotocol%2Finterop?