🚚 Move to MQT Core package

[burgholzer]

Description

This PR replaces the QFR submodule with the newly introduced MQT Core library that subsumes the QFR, DD package, and ZX package. At the moment, this entails no functional changes and only required minor adaptions.

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.

[github-actions]

Cpp-Linter Report ✔️

No problems need attention.

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[burgholzer]

CirrusCI will always fail in PRs like these die to the way how it is configured (it's having problems with the repo rename when switching branches).
Assuming everything works as intended and merging whenever all other checks are green.

[codecov]

Codecov Report

Merging #290 (ab9c5a7) into main (05f1424) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #290     +/-   ##
=======================================
+ Coverage   95.9%   96.1%   +0.1%     
=======================================
  Files         34      34             
  Lines       1721    1721             
  Branches     208     208             
=======================================
+ Hits        1652    1654      +2     
+ Misses        69      67      -2     

Flag	Coverage Δ
cpp	95.7% <100.0%> (+0.1%)	⬆️
python	97.1% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
include/Configuration.hpp	96.2% <ø> (ø)
include/checker/zx/ZXChecker.hpp	100.0% <ø> (ø)
src/EquivalenceCheckingManager.cpp	93.5% <ø> (ø)
src/checker/zx/ZXChecker.cpp	100.0% <ø> (ø)
include/EquivalenceCheckingManager.hpp	100.0% <100.0%> (ø)

... and 2 files with indirect coverage changes