chore: get rid of kv_args and replace it with slices to full_args

[romange]

The main change is in tx_base.* where we introduce ShardArgs slice that is only forward iterable. It allows us to go over sub-ranges of the full arguments slice or read an index of any of its elements.

Since ShardArgs provide now indices into the original argument list we do not need to build the reverse index in transactions.

[dranikpg]

oh no, so much code 📈 🗿

[romange]

Now it's less code