Combine api & serialization into gokzg4844 package

[jtraglia]

This PR will:

• Replace go-proto-danksharding-crypto with go-kzg-4844.
• Update package name at the top of each file.
• Merge errors.go files.
• Remove api. and serialization. in non-test files.
• Replace api. and serialization. with gokzg4844. in test files.
• Move api/* and serialization/* files into the project root.
  • Necessary if you don't want a weird imports like:
  • ✅ import gokzg4844 "github.com/crate-crypto/go-kzg-4844"
  • ❌ import "github.com/crate-crypto/go-kzg-4844/gokzg4844"

Moving the files might be controversial, but it's pretty common. See go-kzg.

[jtraglia]

Ah you're right, I didn't notice that. Will update.