Improve/Repair windows version

[BROKEN] Current windows deployment:
- install visual c++ build tools (VS 2019 cf notes below): https://visualstudio.microsoft.com/downloads/
- install miniconda: https://docs.conda.io/en/latest/miniconda.html#windows-installers
OR mambaforge ? https://github.com/conda-forge/miniforge/releases/latest/download/Mambaforge-Windows-x86_64.exe
- install bocop package with conda (use mamba)

The conda env for windows relies on a specifically built ipopt (3.12) hosted on dtk-forge. Moreover, Visual Studio version is hardcoded to VS 16 2019 in the build() function from bocop.py. This is problematic for instance for the github runners, as the windows-latest image does not have VS 16 anymore. This configuration is hard to maintain and has actually been broken during the build process overhaul (single core lib).

For the future, the aim is to base the windows version on the latest ipopt package from conda-forge. Check the toolchain used (mingw64 ?, msvc ?), and prepare the migration of the conda env accordingly. Also, get rid of the .bat build scripts if possible.