Improve setup process

[raffaem]

This is the result of 2 days of struggle trying to set this up on Windows:

• Changed python3.13 to python in the scripts: for certainty it works also with Python 3.12 and in any case Ubuntu and Windows only have python
• Check errors after activating environments
• Changing pip install to python -m pip install. This is the preferred way to call it since it assures that the pip of the virtual environment is called, and not the global pip
• Removed outdated (?) variable documentation from model_config.py
• Separated setup and run script
• Move dependencies in requirements.txt
• Change IP of infinity from 0.0.0.0 (which has not universally defined meaning and is non standard anyway) to localhost
• Allows to activate virtual environments for both virtualenv/bin (linux and MacOS) and virtualenv/Scripts (Windows) folders
• Running this on Windows under Git Bash will compile Numpy (there is no wheel distribution for this old version of Numpy for this newer version of Python) and so requires MSVC Build Tools and proper environment setup for it. Documented this in README.md.
• Detailed instructions to install and run on Windows natively (without WSL)
• Allow to run your own SearXNG instance without creating a new one (variable START_SEARXNG in model_config.py)

[raffaem]

@SPThole ready for review. This PR will run this natively on Windows (no WSL)