Shadow price configuration in YAML

[sjpfenninger]

Fixes #581

Summary of changes in this pull request:

• Allow enabling shadow price tracking in YAML config.solve
• Only activate shadow price tracking if model is continuous and warn if it is not
• Improved tests for shadow price tracking

Reviewer checklist:

• [ ] Test(s) added to cover contribution
• [ ] Documentation updated
• [ ] Changelog updated
• [ ] Coverage maintained or improved

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.96%. Comparing base (872978d) to head (d984adf). Report is 12 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #587 +/- ## ========================================== + Coverage 95.85% 95.96% +0.10% ========================================== Files 24 24 Lines 3619 3665 +46 Branches 788 735 -53 ========================================== + Hits 3469 3517 +48 + Misses 86 84 -2 Partials 64 64 ``` | [Files](https://app.codecov.io/gh/calliope-project/calliope/pull/587?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=calliope-project) | Coverage Δ | | |---|---|---| | [src/calliope/backend/backend\_model.py](https://app.codecov.io/gh/calliope-project/calliope/pull/587?src=pr&el=tree&filepath=src%2Fcalliope%2Fbackend%2Fbackend_model.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=calliope-project#diff-c3JjL2NhbGxpb3BlL2JhY2tlbmQvYmFja2VuZF9tb2RlbC5weQ==) | `98.07% <100.00%> (+0.16%)` | :arrow_up: | | [src/calliope/backend/pyomo\_backend\_model.py](https://app.codecov.io/gh/calliope-project/calliope/pull/587?src=pr&el=tree&filepath=src%2Fcalliope%2Fbackend%2Fpyomo_backend_model.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=calliope-project#diff-c3JjL2NhbGxpb3BlL2JhY2tlbmQvcHlvbW9fYmFja2VuZF9tb2RlbC5weQ==) | `95.57% <100.00%> (+0.15%)` | :arrow_up: | | [src/calliope/model.py](https://app.codecov.io/gh/calliope-project/calliope/pull/587?src=pr&el=tree&filepath=src%2Fcalliope%2Fmodel.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=calliope-project#diff-c3JjL2NhbGxpb3BlL21vZGVsLnB5) | `93.77% <100.00%> (+0.12%)` | :arrow_up: | | [src/calliope/postprocess/postprocess.py](https://app.codecov.io/gh/calliope-project/calliope/pull/587?src=pr&el=tree&filepath=src%2Fcalliope%2Fpostprocess%2Fpostprocess.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=calliope-project#diff-c3JjL2NhbGxpb3BlL3Bvc3Rwcm9jZXNzL3Bvc3Rwcm9jZXNzLnB5) | `98.24% <ø> (+4.69%)` | :arrow_up: |