Expose write_to_file and compute_iis

[sstroemer]

This is linked to (depends on) this core PR.

This fixes #60.

---

This pull request includes several updates and improvements across multiple files. The changes focus on enhancing functionality, fixing bugs, and updating dependencies. Below are the most important changes:

Enhancements:

• Added a new section in the documentation to explain how to force a solver executable version by explicitly adding the corresponding _jll as a dependency (docs/pages/manual/python/configuration.md).

• Introduced a new method write_to_file in the Model class to write the model to a file, with detailed documentation and examples (src/iesopt/model.py).

• Added a new method compute_iis in the Model class to compute and print the Irreducible Infeasible Set (IIS) of the model, including optional file output and examples (src/iesopt/model.py).

Dependency Updates:

• Updated the IESOPT_CORE, IESOPT_JUMP, and IESOPT_SOLVER_HIGHS versions in the Config class (src/iesopt/config.py).

• Bumped the project version from 2.2.1 to 2.3.0 in pyproject.toml.

Bug Fixes:

• Fixed the key transformation logic in the init method of the Config class to handle keys starting with IESOPT_PKG_ correctly (src/iesopt/config.py).

• Enhanced error logging in the jl_safe_seval function to include exception details (src/iesopt/julia/util.py).

• Improved the setup_julia function to handle exceptions when importing and adding custom Julia packages (src/iesopt/julia/setup.py).

[sstroemer]

The (already anticipated) IESopt core version currently does not exist - after the linked PR is merged and the new release is registered, tests should pass.

[sstroemer]

Note: tests are "passing" but fail due to some sort of juliacall-in-environment issue (that normally requires cleaning the julia env). Does not seem to happen with uv and only with poetry, so merging for now since we will switch anyways.