offchain processing macro and example for sov-nft-module

[dubbelosix]

Description

This PR contains the code for offchain macro which enables creating functions that can update and manage offchain state/computation that doesn't impact on-chain state or consensus.
Decorating a function with the offchain macro causes it to no-op unless the "offchain" feature is explicitly enabled. When the offchain feature is enabled while starting the rollup as described in offchain_readme.md, the code is executed.

Components added

• offchain macro in sov-module-macros
• offchain.rs inside the sov-nft-module for updating postgres tables in sync with transactions
• init_db.sql which has the scripts to create the necessary tables for offchain processing
• utils/nft-utils - a binary that can be used to submit transactions to the sequencer
• simple_client exists with send_transaction, which sends a single transaction in a batch. added send_transactions which takes a vector of transactions, serializes them into a batch and submits to the sequencer. optionally, send_transactions can also take a parameter that controls the batch size. For example Some(3) would mean that multiple batches of up to 3 transactions each are submitted, and None would mean that there is micro batching, and all transactions are submitted.

Outstanding Issues

• There is a timing/concurrency issue with the sequencer and the way it reads from state to accept/reject transactions, so the nft-utils script contains a sleep of 500ms between sends
• sequencer also performs an execute so offchain processing is being done twice. This is not an issue for any of the tables except "top_owners" since the operation is not idempotent (increments are done twice, once in batch_builder and once more in sov_modules_stf_template. investigating options to avoid this double processing

Testing

The script added to create collections and mint NFTs at utils/nft-utils can also be used to test

Docs

Docmentation specific to using and testing the offchain macro is at module-system/module-implementations/sov-nft-module/offchain_readme.md

[codecov]

Codecov Report

Merging #939 (be181d5) into nightly (7229226) will decrease coverage by 1.1%.
The diff coverage is 16.6%.

Files	Coverage Δ
full-node/sov-stf-runner/src/batch_builder.rs	98.0% <100.0%> (+<0.1%)	⬆️
.../module-implementations/sov-nft-module/src/call.rs	97.3% <100.0%> (+0.1%)	⬆️
...m/module-implementations/sov-nft-module/src/lib.rs	96.4% <ø> (ø)
...ule-implementations/sov-nft-module/src/offchain.rs	100.0% <100.0%> (ø)
module-system/sov-modules-api/src/transaction.rs	100.0% <100.0%> (ø)
module-system/sov-modules-macros/src/lib.rs	100.0% <100.0%> (ø)
module-system/sov-modules-macros/src/offchain.rs	100.0% <100.0%> (ø)
full-node/sov-sequencer/src/utils.rs	56.8% <0.0%> (-40.2%)	⬇️
utils/nft-utils/src/main.rs	0.0% <0.0%> (ø)
utils/nft-utils/src/lib.rs	0.0% <0.0%> (ø)

... and 1 file with indirect coverage changes