Remove uniform clearing prices from winner selection

[jmg-duarte]

Description

Uniform clearing prices (UCP) are no longer part of the core CoW Protocol scoring mechanism since CIP-67. In winner selection, the UCP variables were already dead code (_uniform_sell_price / _uniform_buy_price). All scoring uses calculate_custom_prices_from_executed() from per-trade executed amounts instead.

This is the first PR in a series to remove UCP from the entire backend. It targets only the winner-selection crate and its integration points in the autopilot, which is low-risk since the code was already unused.

Changes

• Remove prices: HashMap<Address, U256> field and prices() accessor from winner_selection::Solution
• Remove dead _uniform_sell_price / _uniform_buy_price lookups in compute_order_score()
• Stop passing clearing prices when constructing winsel::Solution in the autopilot
• Set clearing_prices to Default::default() in the run loop (kept to avoid breaking the solver competition API)
• Update test in settlement/mod.rs to match new Solution::new() signature

How to test

1. cargo nextest run -p winner-selection
2. cargo nextest run -p autopilot
3. cargo clippy --locked -p winner-selection -p autopilot --all-features --all-targets -- -D warnings

Staging test

Value	Before	After
0.1	0x749d2	0x13873

[gemini-code-assist]

Code Review

This pull request removes the prices field and its associated logic from the Solution struct across the winner-selection and autopilot crates. Key changes include updating the Solution constructor, removing the prices() getter, and simplifying the compute_order_score function by removing unused uniform clearing price lookups. Additionally, the clearing_prices field in the solver competition API is now defaulted to an empty map to maintain backward compatibility. I have no feedback to provide as the existing review comment was informational and did not meet the required severity or actionability thresholds defined in the style guide.

[MartinquaXD]

Makes sense as the lowest risk first step. 👍