GitLab

* reworked SFNO example

* updated changelog

* Added gradient check to test suite
* reduced size of the unit test
* switched to parametrized for unittests

fixed error in getting started notebook

Adding missing dependency to functoools.partial in sfno.py

Fix __init__.py file to import from local "examples" dir.

Fixing precision mismatch error in weight contractions

Without this fix, importing torch_harmonics had run into a module import error
when trying to execute:
```import examples```

Update __init__.py

Don't import sfno by default (or try/except importing apex)