Use Meson's built-in dependency requirements

Handle unexpected build confusion from earlier today. To summarize, Meson failed to recognize pygobject existence in /usr/lib64/python3.11/site-packages and instead expected an installation through the system's package manager. It took some time to identify as pygobject was correctly installed throught pip, and the current error message did not explicitly indicate what it was expecting. To prevent similar confusion, let's rely on Meson's built-in dependency handling, which provides clearer error messages when dependencies are missing ( in this case, pygobject-3.0. )

In short, this PR will treat python3 and pygobject as hard requirements and will fail accordingly if either is missing.