[nit] Update classifiers

[liamhuber]

Including indicating that the package is stable/production

[github-actions]

👈 Launch a binder notebook on branch pyiron/pyiron_snippets/classifiers

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.12%. Comparing base (6cc2729) to head (704b374).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #68   +/-   ##
=======================================
  Coverage   95.12%   95.12%           
=======================================
  Files          14       14           
  Lines         574      574           
=======================================
  Hits          546      546           
  Misses         28       28           

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