Add ambulance model implementation and docs

[Bluey-Si]

This PR introduces a new ambulance model into simopt. This model setup is based on the ambulance base location problem described in Biased Gradient Estimators in Simulation Optimization (Eckman, D. J. and Henderson, S. G., Proceedings of the 2020 Winter Simulation Conference). I have already reached out to Cen Wang for this PR. Looking forward to feedback and suggestions, thanks!

[cenwangumass]

Hi @Bluey-Si, thanks for the contribution! Can you run ruff check simopt/models/ambulance.py and pyrefly check simopt/models/ambulance.py and fix all the warnings? These warnings are not necessarily errors but need to be fixed for code quality.

[Bluey-Si]

I’ve fixed most of the errors, but I’m keeping the three bad-override errors for dim, lower_bounds, and upper_bounds. These need to be properties rather than classproperty because, like the SAN problem, dim must be dynamically computed based on the model’s factors.

[cenwangumass]

@Bluey-Si, you are absolutely right. This has been fixed in another branch, which will be shortly pushed to master. 1) Can you further run ruff format to reformat the code. 2) With the latest refactor, I have now make all the factors as a Pydantic model. Can you take a look at any example in the models directory and bring your model and problem to that structure. Thanks!

[Bluey-Si]

I've updated the ambulance model to the latest structure and passed previous format checks. Thanks!