Clarify usage and expected structure for BlockData interface in src/ee.ts

[ZKcash-IrishGov]

The BlockData interface is currently marked as TODO and is not implemented. The decodeBlockData function relies on the structure of blockData, but the expected format and required properties are undocumented. Additional information is needed to properly define the BlockData interface and ensure type safety throughout the module.

Please provide details on:

• The intended structure and fields of BlockData
• Example RLP-encoded data to demonstrate typical usage
• Any constraints or edge cases that should be considered when implementing this interface

This will help ensure decodeBlockData and related code can be made type-safe and robust.