Implement Gateway subpackage

[pikonha]

Implement Gateway subpackage

[pikonha]

I think the gateway won't have a connection with any blockchain since its only responsibility is to store data on the database and to accept calls as a smart contract would (see here).

We could indeed use the CCIP-Read-Server but it relies on Ethers v5, which is outdated. A better approach imho would be to implement the CCIP-Read-Server on our own using Ethers v6 or even Viem, which basically receives REST requests following the ERC-3668 standard and maps the function selector with the respective handled, see implementation.

That said, I suggest the goal of this task to be:

• [ ] Implement CCIP-Read-Server using Viem use EVM-Gateway instead
• Implement Gateway API exposing endpoint /{sender}/{data}.json based on ERC-3668

The flow from Client to DB would then be:

1. Client calls setText on contract
2. Client calls Gateway through a REST request like so <url>/<sender>/<calldata>.json
3. Gateway decodes calldata in order to obtain the function selector
4. Find the corresponding API handler
5. Call the handler (MOCK) with the given arguments

P.S: The calldata is composed by function selector and the given arguments
P.S: No further validation is required on the writing phase.