feat: Save sierra program in the runtime

[LucasLvy]

To run the os we need the sierra contract class, it's currently not saved anywhere, save it somewhere that is accessible for the commitment state diff service.

[tdelabro]

I think it should be in the client, not the runtime.
The runtime is supposed to receive the sierra contract and the sierra hash. Check the hash matches the sierra contract, compile the sierra to casm, check the casm hash. But it does not need to be stored for anything else in the runtime.
So, the client can store the contract. It should probably hash it in order to make sure the sierra_hash contained in the tx is the good one.

[tdelabro]

In client, add_declare_transaction, for BroadcastedDeclareTransactionV2 only

• hash the contract_class, make sure it it's hash matches the content of the class_hash field in the tx
• store a mapping from class_hash to contract_class into the madara backend db, in a new db created in crates/client/db
• proceed to publish the tx as usual

Problem with this approach:

• if the tx then fail in the runtime (no accepted in the mempool, execution fails coz no funds), the node would have stored an unusable class. Someone could spam this in order to fill the node disk with garbage class
• it only works for a single node, the others ones won't receive the RPC so they won't be able to replicate this

So I think we should go for something else

[tdelabro]

Another approach:

• Don't change the RPC at all
• when a node receives a block that went through consensus, parse the list of txs, and find the ones that are DeclareTransactionV2 and upper. Do the storing here. No need to check hashes, it should be correct if part of a block. Same DB mapping in the client.

[tdelabro]

closed by #1409