macOS: OBS 18 support

[letmaik]

OBS 18 comes with an updated macOS virtual camera that is incompatible with the previous one.
Therefore, pyvirtualcam needs to be updated to support it.

Users who need to use OBS 17 will have to install an older pyvirtualcam release going forward. Supporting both would be too much maintenance effort.

Compare:
https://github.com/obsproject/obs-studio/tree/27.2.4/plugins/mac-virtualcam/src/obs-plugin
https://github.com/obsproject/obs-studio/tree/28.0.1/plugins/mac-virtualcam/src/obs-plugin

Some initial work was done in https://github.com/letmaik/pyvirtualcam/compare/macos-obs18-support