parallelizable bundle merging algorithm spec

[thegostep]

Performing bundle merging on the relay requires having an algorithm which is able to perform merging in parallel as each bundle is validated in parallel

[fiiiu]

Ran an analysis of bundle "clashes" to guide the algorithm design: https://hackmd.io/hvOkCzxRQu6pJCmcLVzQaQ, which suggests that a minimal merging algorithm should be effective.

Next step is to discuss how to move forward, ideally building some more robust backstesting infra to benchmark the proposed solution against more complete ones.