Feature: Ancestor search

[holke]

Closes #1715

Describe your changes here:

Currently waiting for #1640 to merge.
Will add a description afterwards.

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[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.29%. Comparing base (98a2c07) to head (468ea5a).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/t8_forest/t8_forest_private.cxx	83.33%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1714      +/-   ##
==========================================
+ Coverage   78.25%   78.29%   +0.04%     
==========================================
  Files         114      114              
  Lines       19050    19117      +67     
==========================================
+ Hits        14907    14968      +61     
- Misses       4143     4149       +6     

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[Davknapp]

A first round of remarks! Thanks for this addition!

[Davknapp]

Suggested change

	const t8_locidx_t search_index = t8_forest_bin_search_lower (leafs, element_id + 1, element_id_at_next_level);
	const t8_locidx_t search_index = t8_forest_bin_search_lower (leafs, element_id_at_next_level, element_id + 1);

[holke]

I added the tests for bin_search_upper and lower.

Some doxygen errors show up but they are not related to my added functionality...
I need to finalize a comment in the test.

But, you can finish with the review of the code :)

[holke]

I added a new test for the ancestor search.
Test coverage should now be good.