Allow reth to be used directly to generate test blocks

[Brechtpd]

Describe the feature request

We want to be able to quickly generate test blocks with whatever transactions we need. To do that we can use reth to build blocks. So we need to import reth as a lib, be able to easily create some test transactions/set up the test state, execute the block and then get the required data from get to be able to prove the block.

Kind of related to this: taikoxyz/taiko-reth#2, but also not really.

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