fix(virtualenv): improve virtual environment activation logic

[dannysteenman]

This fix addresses an issue where virtual environments were not activating when opening a terminal directly in a project directory or restarting the shell e.g. exec zsh in the project directory.

for some reason when reloading the shell it would set the .venv bin below the regular python bin in $PATH. This added function will doublecheck if the .venv path is set on top when the shell reloads in the project directory containing the .venv

[hanslemm]

@MichaelAquilina this fixes precisely what described, tested today for the same problem with VSCode terminals: the script didn't autoswitch without the fix that is proposed here.