Test and fix for tensors in marching cubes when Pytorch

[NilsChudalla]

Description

When using Pytorch, Marching cubes algorithm was unable to resolve due to tensor object, where ndarrays should be. This issue occured for scalarfields and in some cases for masks, too. This PR contains the test for pytorch (copied after the existing MC test) and the fix.

Relates to

Checklist

• My code uses type hinting for function and method arguments and return values.
• I have created tests which cover my code.
• The test code either 1. demonstrates at least one valuable use case (e.g. integration tests)
  or 2. verifies that outputs are as expected for given inputs (e.g. unit tests).
• New tests pass locally with my changes.