chore: Move settlement merging to solvers crate

[sunce86]

Background

Currently settlement merging is done in the driver crate. We should consider moving the merging to solvers crate.

Leftover from #1893

[fleupold]

@sunce86 could you give a bit more context on why it's desirable to move the merging logic into the solver crate (why was it put in the driver crate initially and what did we learn since that makes us revisit this choice)? This is not obvious to me from the linked issue.

[sunce86]

Based on the linked issue, it's just a matter of what is whose responsibility. So, if RiskCalculator is part of the solvers, than the merging also needs to be done in solvers so that the success probability is accurately calculated for the merged settlements also. Right now, merged score for merged settlements is just an approximation of what it should be: https://github.com/cowprotocol/services/blob/main/crates/shared/src/http_solver/model.rs#L251-L254

Driver shouldn't do merging. It should just do the encoding, simulations and scoring. It should not generate additional solutions that the solvers is not even aware of.

IMO we can exclude this from the Colocation feature, because the merging was done on SettlementEncoder in the old driver also (so it's not strictly tied to colocation). It should probably be part of the new initiative where we simplify and port the SettlementEncoder into driver::domain.

[github-actions]

This issue has been marked as stale because it has been inactive a while. Please update this issue or it will be automatically closed.