fixed PushBatchStoreStateReq message

[pompon0]

it was pushing the last batch, instead of just a batch number.
Additionally I've:

• tweaked names a bit
• replaced context() with wrap() to propagate cancellation
• fixed gossipnet msg size limits
• added Debug for the public type

[aakoshh]

Great, changing BatchStoreState::last from a SyncBatch to a BatchNumber makes a whole lot more sense then unconditionally pushing all the L2 blocks to gossip peers after each L1 batch whether they need it or not 👍 We discussed this with @brunoffranca and @RomanBrodetski on standups but none of us were sure whether it's intentional, although the fact that the .proto file said it was a "QC" made it suspicious that it was a copy paste error from the similar block related artifacts.

Perhaps the title can be updated to reflect this change as it will also have to be fixed on the era side, ie. a bit more significant than a nit.