added hexagonal and goldene

[zerothi]

These structures are newly synthesized 2D flat structures.

• [x] Added tests for new/changed functions?
• [x] Ran isort . and black . [24.2.0] at top-level
• [x] Documentation for functionality in docs/
• [x] Changes documented in CHANGELOG.md

[codecov[bot]]

Codecov Report

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

Project coverage is 86.78%. Comparing base (1cf5a94) to head (6ad8686).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #752 +/- ## ======================================= Coverage 86.78% 86.78% ======================================= Files 412 412 Lines 51954 51967 +13 ======================================= + Hits 45088 45101 +13 Misses 6866 6866 ```

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