build: Add type annotations for CustomTarget constructor
build: Add type annotations for CustomTarget constructor

which are needed in the rust module for bindgen support.

pexip/meson,mesonbuild/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,QuLogic/meson,pexip/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,jpakkane/meson,mesonbuild/meson,jpakkane/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,QuLogic/meson,pexip/meson,QuLogic/meson,jpakkane/meson,QuLogic/meson,QuLogic/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,QuLogic/meson,QuLogic/meson,mesonbuild/meson,QuLogic/meson,pexip/meson,jpakkane/meson,QuLogic/meson,jpakkane/meson,pexip/meson,mesonbuild/meson