New tranching approach

[tsmbland]

Description

Implements the second tranching idea discussed in #1358 (at the bottom), which uses a dynamic capacity approach, where candidate asset capacities are set according to annual demand:

capacity = capacity_limit_factor * annual_demand / max_annual_supply_per_capacity

This is similar to the current demand-limiting-capacity approach, but slightly safer as it cannot be throw off by extreme demand/availability values in any particular timeslices.

Also changing capacity_limit_factor to 0.05, as suggested by Adam, but we may change this after more testing

Based on a discussion with Adam on teams, we've decided that divisible assets should be appraised one unit at a time.

I've had to turn off tests for circularity and circularity_npv as these are failing. We have an issue open for this (#1368).

Fixes #1358

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
• Update release notes for the latest release if this PR adds a new feature or fixes a bug
  present in the previous release

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 86.77%. Comparing base (3334eb5) to head (ce1fad6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1395      +/-   ##
==========================================
- Coverage   89.42%   86.77%   -2.66%     
==========================================
  Files          58       58              
  Lines        8367     8376       +9     
  Branches     8367     8376       +9     
==========================================
- Hits         7482     7268     -214     
- Misses        564      792     +228     
+ Partials      321      316       -5     

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[Copilot]

Pull request overview

Implements a revised tranching approach for candidate asset sizing in the investment loop by assigning candidate capacities from an annual-demand-based characteristic capacity scale, then applying capacity_limit_factor as the per-round appraisal fraction.

Changes:

• Add an annual-demand-based capacity scaling helper and use it to size candidate assets during option generation.
• Adjust the default capacity_limit_factor (0.1 → 0.05) to reflect the new capacity scaling behaviour.
• Update the model schema documentation for capacity_limit_factor to describe the new meaning.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/simulation/investment.rs	Introduces annual-demand-based candidate capacity scaling and adds tests around the new helper.
src/model/parameters.rs	Changes the default value of capacity_limit_factor to align with the new tranching increments.
schemas/input/model.yaml	Updates schema docs/default for capacity_limit_factor to match the new candidate sizing approach.

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[tsmbland]

There will be more to add to the release notes. Best to do this just before making a release, as we've done in the past.