Add optional depencies for Torch backend (#9)

* Add optional depencies for Torch backend

* Remove unnecessary torch dependencies

---------

Co-authored-by: Jaron Maene <Jaron.maene@gmail.com>

Author: rmanhaeve

pyproject.toml

@@ -18,6 +18,12 @@ classifiers = [
     "License :: OSI Approved :: Apache Software License",
 ]
 
+[project.optional-dependencies]
+torch = [
+    "torch",
+]
+
+
 [project.urls]
 Homepage = "https://github.com/ML-KULeuven/klay"