NubitDA integration

[sieniven]

Summary

• Development on NubitDA integration as X Layer validium node's offchain data availability provider
• Implementation of Nubit's core team development on Polygon's cdk-validium-node integration demo: https://github.com/RiemaLabs/cdk-validium-node]
• Fixes on PR Port nubit integration fixes RiemaLabs/cdk-validium-node#2 is on the X layer node's integration as well

Nubit backend implementation fixes

• Add encoding scheme for encoding L2 batches data into NubitDA blobs that will subsequently be sent to NubitDA layer
• Add encoding scheme for encoding NubitDA blob data into dataAvailabilityMessage
• Use geth abi library for encoding NubitDA blobs for on-chain decoding using default ABI encoding
• Resolve issue on GetSequence pipeline - the old backend implementation does not handle the decoding of data availability message correctly (as it was changed to sequence signature)
• Using the encoding scheme for NubitDA blob data, getSequence pipeline is fixed and blobs are able to be retrieved using their metadata from the Nubit network, using the on-chain data availability message in batch txs

Refactor changes

• Revert back to the original PostSequence interface - theres no need to change the interface since sequences are signed by the sequence sender private key. Also, we should maintain interfaces for backwards compatibility
• Add configurable callbacks for blob confirmation on NubitDA layer in post sequence pipeline
• Minor fixes - code cleanups, better error handling

[sieniven]

cc/ @archidoge0