🚸 add configurable repo owner for mqt-core dependency

[burgholzer]

Description

This small PR adds a configuration option for the owner of the mqt-core dependency that is fetched via FetchContent. This should make it easier to point to forks of mqt-core.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.5%. Comparing base (cfd2f65) to head (b428147).
Report is 62 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #392     +/-   ##
=======================================
- Coverage   92.5%   92.5%   -0.1%     
=======================================
  Files         37      37             
  Lines       2561    2561             
  Branches     310     310             
=======================================
- Hits        2371    2370      -1     
- Misses       190     191      +1     

Flag	Coverage Δ
cpp	94.5% <ø> (-0.1%)	⬇️
python	87.3% <ø> (ø)

see 1 file with indirect coverage changes