Default installation python -m pip install gdsfactory requires kfactory

[sebastian-goeldi]

Describe the bug
The default installation now requires kfactory due to the default import of difftest. This results in a package that when installed freshly doesn't work and crashes on import.

To Reproduce
python -m pip install gdsfactory in a fresh environment

Expected behavior
The package should install in a working condition by default

Suggested fix
Either add kfactory as a dependency or make the import of difftest not default and add a warning when trying to import without having kfactory installed

[joamatab]

Hi Sebastian,

In the difftest I added try, except
#1712

How does that sound?

[sebastian-goeldi]

LGTM 👍