feat: add vesta viewer

[stevenhua0320]

@sbillinge ready to review. With the assistance of Claude code (with some training to group standard), it mimics the original atomeye app viewer and writes a vesta viewer. Moreover, since vesta supports its specific file format vesta, I also added a p_vesta for the parser with file that ends with vesta.

Additionally, I noticed that I missed one call of snakecase method (abcABG to cell_params), therefore, I also changed it in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.20%. Comparing base (4f7656c) to head (05c0219).
⚠️ Report is 3 commits behind head on v3.4.0.

Additional details and impacted files

@@           Coverage Diff           @@
##           v3.4.0     #188   +/-   ##
=======================================
  Coverage   99.20%   99.20%           
=======================================
  Files          15       15           
  Lines        2501     2501           
=======================================
  Hits         2481     2481           
  Misses         20       20           

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[sbillinge]

Thanks @stevenhua0320. Did you review the code and clean it up before sending? You may want to take a look and save me some time.

[stevenhua0320]

Yes, I took the review of the code and did a bit cleaning for the code structure. I think the logic is right. Since we don't have a command line control to test this one, we might need to integrate it into diffpy.cmi and test whether the functionality of the viewer works properly.