fix(cucumber): handles listHeaders response correctly

[sdbondi]

Description

• Fixes how listHeaders GRPC response is handled (since feat: merge grpc list headers commands #4515)

Motivation and Context

#4515 returns the header in a nested struct, this PR updates the js code to handle that correctly.

How Has This Been Tested?

Pruned node should prune outputs passes

[sdbondi]

This is partially solved in #4552, however there are still cases where the new list headers return structure is not handled - I'll update the code here as needed, which may involve undoing #4552 (as getTipHeader is changed here to return the "non-nested" header). There were also a few other places where getTipHeader return type wasn't changed.