Define new types

[tbenr]

There are several new types defined in the spc. When these types are just alias of a generic type we use the generic one. But if these types are more complex or requires specific validation we have to create a specific class.

from polynomial commitments types we need to define:

• KZGCommitment we need an ssz version of it like SszPublicKey (will be in BeaconBlockBody schema to build a list of them via SszListSchema.create(KZGCommitment, ...))
• KZGProof we need an ssz version of it like SszPublicKey (will be part of BlobsSidecar schema)
• Blob we need an ssz version defined via SszByteVectorSchema.create() (will be part of BlobsSidecar schema as SszListSchema.create(Blob, ..))