⬆️ update mqt-core

[burgholzer]

Description

This PR updates the mqt-core submodule and brings in some further advancements from #355.
Specifically, it switches to using FetchContent for obtaining mqt-core.
Per default, it is pointed to the vendored submodule via an overridable CMake variable.

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 ✅

Comparison is base (f6cc523) 96.3% compared to head (3a2cdb2) 96.1%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #357     +/-   ##
=======================================
- Coverage   96.3%   96.1%   -0.3%     
=======================================
  Files         34      34             
  Lines       1753    1754      +1     
  Branches     215     215             
=======================================
- Hits        1689    1686      -3     
- Misses        64      68      +4     

Flag	Coverage Δ
cpp	95.8% <ø> (-0.3%)	⬇️
python	97.2% <ø> (ø)

see 2 files with indirect coverage changes