Improve the TensorNet model class coverage

[kenko911]

Summary

A unit test is added for testing SO(3) equivariance to improve the coverage.

Checklist

• [x] Google format doc strings added. Check with ruff.
• [x] Type annotations included. Check with mypy.
• [x] Tests added for new features/fixes.
• [x] If applicable, new classes/functions/modules have duecredit @due.dcite decorators to reference relevant papers by DOI (example)

Tip: Install pre-commit hooks to auto-check types and linting before every commit:

pip install -U pre-commit
pre-commit install

[codecov[bot]]

Codecov Report

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

Project coverage is 98.29%. Comparing base (c612f62) to head (93574e0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #276 +/- ## ======================================= Coverage 98.29% 98.29% ======================================= Files 35 35 Lines 3117 3117 ======================================= Hits 3064 3064 Misses 53 53 ```

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