Add test utility to validate whether the generated block includes a builder txn

[ferranbt]

[owizdom]

hey, guys,

i saw this issue stil open and decided to build a test utility for validating whether the generated block includes a builder txn. it’s a rust library and cli tool that checks if blocks contain the expected builder transaction with "block number: {}" in the input data as a transfer to the zero address.

i wanna work on this !! @ferranbt