Finish pybind11 dependence removal

[michael-petersen]

This pull request improves support for disabling the Python development environment by making the build system respect the DISABLE_PYTHON option throughout the CMake configuration. The changes ensure that Python-related dependencies and targets are only included when Python support is enabled, resulting in a cleaner and more robust build process when Python is not required.

Build system improvements for Python support:

• Added logic in CMakeLists.txt to set ENABLE_PYEXP to OFF and print a status message when DISABLE_PYTHON is enabled, preventing the build of Python-related components.
• Conditionalized inclusion of pybind11 headers and subdirectory in the main CMakeLists.txt and only add them if Python is not disabled.
• Updated exputil/CMakeLists.txt to only link against pybind11::embed if Python support is enabled, avoiding unnecessary dependencies.

Test utilities adjustments:

• Modified utils/Test/CMakeLists.txt to only add and link the testEmp executable (and its dependencies) if Python is enabled, ensuring test targets are consistent with the build configuration.

Minor code improvement:

• Added a missing #include <cassert> in exputil/realize_model.cc for improved code safety and correctness.

[michael-petersen]

This PR helps the work started by @Leengit, if you'd also like to take a look?

[Copilot]

Pull request overview

This PR updates the CMake build to better support configurations where the Python development environment is disabled (DISABLE_PYTHON=ON), by conditionally excluding Python-related dependencies/targets and adjusting one C++ source include.

Changes:

• Gate inclusion of the extern/pybind11 subdirectory and headers on DISABLE_PYTHON.
• Avoid linking pybind11::embed (and avoid building/linking the testEmp test utility) when Python is disabled.
• Add a missing <cassert> include in exputil/realize_model.cc.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
CMakeLists.txt	Adds DISABLE_PYTHON handling and conditionally includes/adds extern/pybind11.
exputil/CMakeLists.txt	Conditionally links pybind11::embed only when Python is not disabled.
utils/Test/CMakeLists.txt	Conditionally builds/links testEmp only when Python is not disabled.
exputil/realize_model.cc	Adds <cassert> include to support existing assert(...) usage.

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[The9Cat]

Do we have a use case for the resulting build that can be tested and verified? @Leengit may have already done this?

[michael-petersen]

I've built this version of the code on tursa, which has effective no Python (a version so old it can't handle pybind11). So I think that's sufficient testing, unless we get any external input.

[The9Cat]

Agreed.