add time-averaged values

[keiyamamo]

• compute time averaged displacement/velocity/pressure during the simulation and save it in the Visualization folder.
• Use save_solution_after_tstep to specify when to start sampling the data.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.33333% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 79.00%. Comparing base (a7878b2) to head (b04e954).

Files	Patch %	Lines
src/vasp/simulations/aneurysm.py	83.33%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #164 +/- ## ========================================== + Coverage 78.98% 79.00% +0.01% ========================================== Files 34 34 Lines 3760 3781 +21 ========================================== + Hits 2970 2987 +17 - Misses 790 794 +4 ```

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