Previously I tried to check whether I2P is ready by looking for the
green star next to the Shared Client Tunnel entry. Unforunately,
however, Sikuli couldn't tell the difference between a green star and a
yellow one.

With recent versions of I2P, there are two shared client tunnel entries,
one for the old DSA encryption and one for modern edDSA. When *both*
entries are visible, I2P should be ready to use. This should be much
more reliable than checking whether port 4444 is open, especially since
the static sleep added to work around the upstream bug does not work
when the function is called from the shell library.