Add Grandine FOCIL project proposal by Subhasish Behera

[Subhasish-Behera]

This PR adds my EPF7 project proposal for implementing EIP-7805 (FOCIL) in Grandine.

The proposal covers the end-to-end Heze implementation, including inclusion-list production and networking, Engine API
integration, fork-choice enforcement, validator duties, testing, and cross-client interoperability.

[taxmeifyoucan]

Thanks for the proposal! It seems well researched and technically sound.

I have only some minor concerns - first the flow of the document and length. Lot's of repetitive points between project description, specs section and roadmap, feels like a big part could be better said in your own words without so much repetition. I mean no need to directly copy the focil spec, lot of text is just spec restatement and enumeration.
Second thing is the scope and roadmap, it is rather optimistic considering the current state of development and in comparison to focil in lighthouse project, their project has 2 fellows working on it. It's a lot of work so I would think more about what is basic deliverable and stretch goals

[Subhasish-Behera]

Hey @taxmeifyoucan, I don’t have any problem with the suggestions. For 2, the FOCIL devnet prep has already been announced (https://discord.com/channels/595666850260713488/892088344438255616/1537022531083706419) and is close, so whether I’ll be completing the implementation end-to-end myself or getting help from the Grandine team will mostly depend on the dates. But I’m unlikely to move in a parallel implementation/PoC direction, as initial development has been tested against the latest spec. Will inform if this changes.

The dates I have currently estimated are based on the fact that the Gloas implementation from scratch took 7 months to hit from the first commit to the glamstredam devnet in Grandine. The complexity of FOCIL on the CL side across various factors like new containers, functions, impacted beacon state, less intrusive changes and fork choice adaptation can be estimated as <1/3 the complexity of Gloas for now. But for the proposal, i. can shift the written dates of the hardening/interop to the post-EPF stretch. 
(The context is FOCIL-specific(not braoder Heze) dates)

[Subhasish-Behera]

@taxmeifyoucan removed the repetitions and changed the roadmap to put testing/interop post-EPF. please let me know if more changes are required. Thanks