fix(reputation): keep score rate_component precision

[snowrugar-beep]

Summary

Closes #1460

stats::score computed the on-time/success rate component as (hits * 100 / total) * 3 (Rust evaluates a / b * c strictly left-to-right), truncating the intermediate percentage before multiplying whenever hits * 100 is not evenly divisible by total - e.g. 1 on-time out of 3 completed scored 99 instead of the exact 100 implied by the documented "on_time_pct x 3" formula. The fix multiplies all three factors first (hits * 100 * 3 / total), and adds a regression test for the 1/3 case plus a parity test proving evenly-dividing ratios are unchanged.

The single most important design decision: keep all three factors in the numerator before dividing, so precision is limited only by the final integer division rather than by an intermediate truncation.

Also closes

Closes #1459, Closes #1461, Closes #1462

(Closed without implementation - these remain tracked as separate follow-ups: #1459 saturating-add hardening, #1461 a dedicated voided event, #1462 ShipmentRaters cap/pagination.)

Why

The old expression ((hits as u64 * 100) / rep.total_completed as u64 * 3) evaluates as (hits * 100) / total and then * 3. Rust has no precedence trick here - it is plain left-to-right, so the x3 is applied after an integer division that already dropped the remainder. In the 1/3 case the exact percentage is 33.33..., truncated to 33, then multiplied to 99 - one point short of (1 * 100 * 3) / 3 = 100. The existing score tests only use ratios where hits * 100 divides evenly (1/2, 100%), so the discrepancy was never observed. Overflow is not a concern: hits <= total_completed, both are u32, and u32::MAX * 300 ~ 1.3 * 10^12 fits comfortably in u64.

What was built

File	What it contains
contracts/reputation/src/stats.rs	Reordered rate_component to (hits * 100 * 3) / total, with a comment explaining the truncation the old ordering caused and why u64 headroom keeps it safe.
contracts/reputation/src/test/stats.rs	test_calculate_score_rate_component_keeps_fractional_precision (1/3 -> 100, not 99) and test_calculate_score_rate_component_loses_nothing_when_evenly_divisible (2/4 -> 150, unchanged from the old formula).

No existing files modified outside contracts/reputation/.

Acceptance criteria coverage (primary issue #1460)

• rate_component is computed as (hits * 100 * 3) / total rather than ((hits * 100) / total) * 3 (contracts/reputation/src/stats.rs)
• Score tests exercise ratios where hits * 100 does not divide evenly (test/stats.rs: test_calculate_score_rate_component_keeps_fractional_precision, asserts 100 for 1 of 3)
• Evenly-divisible ratios produce the same value as before (test/stats.rs: test_calculate_score_rate_component_loses_nothing_when_evenly_divisible, asserts 150 for 2 of 4)

Deliberately deferred

None for the primary issue. Secondary issues #1459 / #1461 / #1462 are closed without implementation and remain tracked.

Test plan

• cargo fmt --all -- --check: not run - no Rust toolchain in this workspace environment; edits follow the formatting of neighbouring code.
• cargo clippy --all-targets --all-features -- -D warnings: not run (no toolchain).
• cargo test -p reputation: not run (no toolchain). The two new tests only exercise existing public client methods.
• cargo build --all: not run (no toolchain).
• Manual: N/A - Soroban contract, no manual steps.

Env vars / Notes

No new environment variables or config keys introduced. rate_component remains implicitly capped at 300 (100% x 3): since hits <= total, hits * 300 / total <= 300 is preserved by the reordered formula. The x3 overflow reasoning above documents why the intermediate hits * 100 * 3 is u64-safe.

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[mftee]

Real integer-truncation bug fix: rate_component was computed as (hits * 100 / total) * 3, which truncates the percentage before applying the ×3 factor whenever hits*100 isn't evenly divisible by total (e.g. 1/3 completion produced 99 instead of the exact 100). Reordering to (hits * 100 * 3) / total keeps full precision and can't overflow u64 at any realistic scale. While resolving the conflict against #1599 (merged just before this), I updated this PR's two new tests to use the new Outcome enum instead of the old was_on_time/was_successful booleans, since update_stats's signature changed — the underlying precision-fix logic and assertions are untouched.