feat: add FIX descriptor engine integration

[swapnilraj]

Summary

• add FixDescriptorEngine core contract plus module interface/wrapper to expose descriptor-driven metadata.
• provide deployment-ready FIX variants of standalone and upgradeable CMTAT contracts (including UUPS).
• supply mocks and test harnesses covering descriptor registration, CBOR validation, and module wiring.
• update Hardhat configuration and package manifests so builds/test suites include the new FIX engine.

Design

• Specification for the original erc-fix.com/spec adapted for the CMTAT contracts
• FIX descriptor logic keeps CBOR storage off-chain; contracts only ingest hashes and pointers, keeping deployment costs flat.
• Wrapper module isolates descriptor engine behind IFixDescriptorEngineModule, so existing deployments can toggle the feature with minimal surface change.
• Deployment contracts compose the base modules rather than duplicating logic, preventing drift with non-FIX variants.

[rya-sge]

Hello @swapnilraj ,

Thanks a lot for your PR, great work !

Some questions:

1. Engines are generally put in a dedicated repository. Is it Ok for you if we create a new repository inside CMTA so you can add the engine here ?

2. Do you have planned to keep fix-descriptor in your GitHub or it will move to a GitHub managed by an organisation ?

Due to the dependence with the SDK, I will be more favorable if we put all the fix dedicated smart contracts (including modules and deployment version) in a dedicated repository instead of the main CMTAT repository.
In this case, we could have the engine and all CMTAT related modification in the same repository.

We already do this for the SnapshotEngine, which also contains a specific deployment version with modules for CMTAT: SnapshotEngine

This dedicated repository could be host in your GitHub or in CMTA organisation as you prefer.

Feel free to contact me on X if you have questions

[rya-sge]

As discussed, the code will be moved to a dedicated repository: CMTAT-FIX

[swapnilraj]

Hey @rya-sge as agreed we are continuing this work in the CMTAT-FIX repo
CMTAT-FIX

and we are working on integration PR needed for the CMTAT repo