Fix: Use consistent ordering for commodity prices between runs

[alexdewar]

Description

While working on #595 I noticed that commodity prices were in a random order after we removed the contents of CommodityPrices::add_from_solution and were therefore all being added (as NaN) in add_remaining. The issue is that we're using a HashSet to store the IDs of commodities without prices, so, while CommodityPrices retains insertion order (being an IndexMap), its contents can end up in a random order anyway. We just didn't notice before because we only had one commodity without a price.

There are different ways we could fix this, but I've opted to change CommodityPrices to use a BTreeMap rather than an IndexMap, so the contents are kept ordered according to the commodity ID (i.e. alphabetically). It doesn't particularly matter, but doing it this way means that the commodities are consistently in the same order for different milestone years, which seems like a nice property to have.

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.54%. Comparing base (d7fc05f) to head (091e015).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #601      +/-   ##
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+ Coverage   84.51%   84.54%   +0.03%     
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  Files          37       37              
  Lines        3255     3255              
  Branches     3255     3255              
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+ Hits         2751     2752       +1     
+ Misses        318      317       -1     
  Partials      186      186              

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[Copilot]

Pull Request Overview

This PR ensures commodity prices are stored in a consistent, sorted order by switching from an IndexMap to a BTreeMap and deriving the necessary ordering traits on key types.

• Derive Ord/PartialOrd on TimeSliceID and all ID types to support ordering.
• Replace IndexMap with BTreeMap for CommodityPrices.
• Update imports and macro-derived traits for ID types.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/time_slice.rs	Added Ord/PartialOrd derives to TimeSliceID
src/simulation/prices.rs	Swapped IndexMap for BTreeMap in CommodityPrices
src/id.rs	Extended define_id_type! to derive Ord/PartialOrd

Comments suppressed due to low confidence (3)

src/simulation/prices.rs:13

• Consider adding a unit test that inserts a known set of commodity IDs and asserts the iteration order remains consistent across runs when using BTreeMap.

pub struct CommodityPrices(BTreeMap<(CommodityID, RegionID, TimeSliceID), f64>);

src/simulation/prices.rs:11

• [nitpick] Update this doc comment to note that the map now enforces sorted key ordering by commodity ID for deterministic output.

/// A map relating commodity ID + region + time slice to current price (endogenous)

src/simulation/prices.rs:9

• [nitpick] Switching from IndexMap (O(1) operations) to BTreeMap (O(log N) operations) may affect performance; consider benchmarking if the map grows large.

use std::collections::{BTreeMap, HashSet};

[tsmbland]

Seems reasonable!