Fix: Use virtual environment for Python dependencies in documentation workflow

[DigraJatin]

Fixes #77

Issue -
The documentation workflow was failing due to:

1. Homebrew deprecating the doxygen cask in favor of the formula
2. Python PEP 668 preventing system-wide pip installs on macOS

Fix done -

• Use brew install doxygen (formula instead of cask)
• Create a Python virtual environment for installing jinja2 and Pygments
• Activate venv in both install and build steps

Testing -
Tested on my fork by creating a tag, documentation workflow completes successfully.

[DeveloperPaul123]

Looks good to me! Nice work 👍