docs: finalize SSZ usage documentation for TypeScript devs (Issue #5045)

[lolosaisa]

This PR adds a rough structure for the SSZ documentation targeted at TypeScript developers, in reference to #5045.

What's included

• Created /packages/types/docs/ directory to hold new SSZ usage documentation
• Added placeholder files for:
  • ssz-quickstart.md – Quickstart on serialize/deserialize/hashTreeRoot
  • ssz-views-and-proofs.md – Overview of views and merkle proofs
• Introduced per-phase folders and files for documenting specific SSZ types:
  • phase0/Attestation.md, BeaconBlock.md, Validator.md
  • altair/SyncCommittee.md
  • bellatrix/ExecutionPayload.md
• Draft README.md outlining the purpose and structure of the documentation

Purpose

This PR is intended to:

• Propose a clean and scalable folder/file structure for upcoming documentation
• Demonstrate commitment to the issue
• Invite feedback and approval from maintainers before continuing with full content development

Full examples and in-depth code explanations will be added in follow-up PRs once this structure is reviewed and accepted.

---

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.72%. Comparing base (d50b3b7) to head (f644b08).
Report is 2 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #8078      +/-   ##
============================================
- Coverage     55.72%   55.72%   -0.01%     
============================================
  Files           834      834              
  Lines         59754    59771      +17     
  Branches       4611     4613       +2     
============================================
+ Hits          33299    33306       +7     
- Misses        26386    26396      +10     
  Partials         69       69              

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[lolosaisa]

This PR completes the SSZ documentation targeted at TypeScript developers.

What's New

• Finalized README.md explaining the documentation purpose and structure
• Added ssz-quickstart.md — beginner-friendly introduction to SSZ
• Added ssz-views-and-proofs.md — advanced guide on tree-backed views and proofs
• Included runnable TypeScript examples and detailed explanations in the ssz-examples.md
• Improved clarity, fixed broken links, and standardized file structure
  Ready for review