EIP-3651 Warm Coinbase

Documentation for tests/shanghai/eip3651_warm_coinbase.

Generate fixtures for these test cases with:

fill -v tests/shanghai/eip3651_warm_coinbase

abstract: Tests EIP-3651: Warm COINBASE

Tests for [EIP-3651: Warm COINBASE](https://eips.ethereum.org/EIPS/eip-3651).