deep copy the volume transform

[alessandrofelder]

Description

What is this PR

• [x] Bug fix
• [ ] Addition of a new feature
• [ ] Other

Why is this PR needed? There's a small bug in the test_volumetric_data transformation.

References

Fixes #294

How has this PR been tested?

Only on CI, by re-enabling the relevant test through the GH UI.

Is this a breaking change?

No

Does this PR require an update to the documentation?

No

Checklist:

• [ ] The code has been tested locally
• [x] Tests have been added to cover all new functionality (unit & integration)
• [x] The documentation has been updated to reflect any changes
• [x] The code has been formatted with pre-commit

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7d00370) 86.24% compared to head (4c3b590) 86.24%. Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #297 +/- ## ======================================= Coverage 86.24% 86.24% ======================================= Files 26 26 Lines 1214 1214 ======================================= Hits 1047 1047 Misses 167 167 ```

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