ufunclab uses meson-python (and therefore meson and ninja) as its
build system.
To install the source with the git repository checked out, it should be sufficient to run
$ pip install .
To develop locally, I've been using this in the checked out repository:
$ meson setup build --prefix $(pwd)/build-install
$ cd build
$ ninja
$ ninja install
That will install the package in the build-install directory.
Note: I'm not a meson expert. In fact, I'm probably Using It Wrong. If you see incorrect or inefficient uses, create an issue on github and let me know.