WIP: Update ACE to ACEpotentials 0.6.9

[juraskov]

This PR is an update of the rather outdated ACE version in mlptrain to ACEpotentials 0.6.4. This is not the latest version of the packages, but the version recommended by developers (i.e., within 0.6.x). An update to 0.8 versions would require some changes in the syntax.
TODO list:

• Customization of basis function
• Correct interface to ASE
• Parallelization
• Sensible defaults
• Tests against the old ACE version
• More solvers

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 64.56%. Comparing base (3cb0ddb) to head (c314594).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
mlptrain/potentials/ace/ace.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
- Coverage   64.75%   64.56%   -0.19%     
==========================================
  Files          37       38       +1     
  Lines        4298     4315      +17     
==========================================
+ Hits         2783     2786       +3     
- Misses       1515     1529      +14     

Flag	Coverage Δ
python-3.10	60.62% <0.00%> (?)
python-3.10-mace	64.38% <0.00%> (?)
python-3.9	?
python-3.9-ace	?
python-3.9-mace	?

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