Collapse settlement metrics into single-pass summarize()

[ashleychandy]

Description

Previously, computing settlement metrics required four separate iterations
over the trades collection — one each for surplus_in_ether(),
fee_in_ether(), fee_breakdown(), and jit_orders():

let gas = settlement.gas();
let gas_price = settlement.gas_price();
let surplus = settlement.surplus_in_ether();
let fee = settlement.fee_in_ether();
let fee_breakdown = settlement.fee_breakdown();
let jit_orders = settlement.jit_orders();

This PR introduces a summarize() method on Settlement that performs a
single pass over self.trades, accumulating all four values simultaneously
and returning them as a SettlementMetrics<'_> struct. The call site in
infra/persistence is updated to destructure directly from the returned struct:

let domain::settlement::SettlementMetrics {
    gas,
    gas_price,
    surplus,
    fee,
    fee_breakdown,
    jit_orders,
} = settlement.summarize();

The returned struct is defined as:

#[derive(Debug)]
pub struct SettlementMetrics<'a> {
    pub gas: eth::Gas,
    pub gas_price: eth::EffectiveGasPrice,
    pub surplus: eth::Ether,
    pub fee: eth::Ether,
    pub fee_breakdown: HashMap<domain::OrderUid, trade::FeeBreakdown>,
    pub jit_orders: Vec<&'a trade::Jit>,
}

Changes

• domain/settlement/mod.rs

  • Added SettlementMetrics<'a> struct
  • Added Settlement::summarize() — single-pass computation replacing
    the four individual iteration methods
  • Preserves existing tracing::warn! fallback behaviour on per-trade errors

• infra/persistence/mod.rs

  • Replaced six individual settlement.*() calls with a single
    settlement.summarize(), destructuring all fields directly from
    SettlementMetrics via pattern matching

Fixes #4346

[gemini-code-assist]

Code Review

This pull request optimizes settlement metric calculations by introducing a SettlementMetrics struct and a summarize method that performs a single pass over trades. This replaces four separate iterations previously used to compute surplus, fees, and JIT orders. The persistence layer was updated to use this more efficient approach. No critical issues found.

[jmg-duarte]

Much easier to review, thanks for the effort!

Some notes though

[ashleychandy]

@jmg-duarte thanks for the detailed review, I’ve addressed the comments:

removed the now-unused individual metric functions
simplified the summarize docs
restricted SettlementMetrics fields to pub(crate)
removed the redundant inline comments in the loop

[jmg-duarte]

I expect this to be the final list of notes, will run CI as well

[jmg-duarte]

I didn't notice this one, but again, not needed

[jmg-duarte]

LGTM