feat: make SSZVector of Fp serializable

[unnawut]

🗒️ Description

I was having issue with getting #193 to output the signatures to test vectors. It looks like SSZVector didn't know how to serialize Fp. 3 main changes are done:

• Fp.__get_pydantic_core_schema__() is implemented similar to BaseUint.__get_pydantic_core_schema__() Reverted. Turns out it's not needed anymore
• SSZVector._serialize_data() is implemented similar to SSZList._serialize_data()
• SSZList._serialize_data() updated to support handling Fp items (only for consistency)

See how they are being used in #193.

🔗 Related Issues or PRs

✅ Checklist

• Ran tox checks to avoid unnecessary CI fails:

  uvx tox

• Considered adding appropriate tests for the changes.
• Considered updating the online docs in the ./docs/ directory.

[tcoratger]

Can we have some small unit tests for this?

Even if this is pretty obvious, that is probably better to have tests in order to confirm that nothing is broken in the future with this.

[unnawut]

@tcoratger Sorry I forgot to add. Would this be enough? 728f736

[tcoratger]

Thanks a lot :)