🚸 Installation Improvements

[burgholzer]

Description

This PR improves a couple of bits and pieces throughout the library and should increase the overall usability and DX.

Most notable breaking changes:

• The MQT::CorePython target is removed. After this PR is merged, top-level packages are expected to use the mqt.core Python package for translating from Qiskit to MQT. Furthermore, the top-level packages are responsible for bringing in the pybind11_json dependency if they require it, as it is no longer shipped with mqt-core.
• The MQT::ProjectOptions and MQT::ProjectWarnings targets are now linked privately into the libraries in order to not pollute other CMake targets. This means that top-level projects now also need to explicitly link against these targets if they want to benefit from the common settings.
• Includes are now placed in a dedicated include/mqt-core subdirectory to create a cleaner installation structure.

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 (6d9a08e) 91.2% compared to head (889ac89) 91.2%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #539     +/-   ##
=======================================
- Coverage   91.2%   91.2%   -0.1%     
=======================================
  Files        130     130             
  Lines      13709   13709             
  Branches    2155    2155             
=======================================
- Hits       12510   12509      -1     
- Misses      1199    1200      +1     

Flag	Coverage Δ
cpp	90.9% <ø> (ø)
python	99.5% <100.0%> (-0.3%)	⬇️

Files	Coverage Δ
include/mqt-core/CircuitOptimizer.hpp	100.0% <ø> (ø)
include/mqt-core/Definitions.hpp	76.4% <ø> (ø)
include/mqt-core/Permutation.hpp	100.0% <ø> (ø)
include/mqt-core/QuantumComputation.hpp	91.6% <ø> (ø)
...qt-core/algorithms/GoogleRandomCircuitSampling.hpp	58.3% <ø> (ø)
include/mqt-core/dd/Benchmark.hpp	85.7% <ø> (ø)
include/mqt-core/dd/CachedEdge.hpp	85.7% <ø> (ø)
include/mqt-core/dd/Complex.hpp	100.0% <ø> (ø)
include/mqt-core/dd/ComplexNumbers.hpp	100.0% <ø> (ø)
include/mqt-core/dd/ComplexValue.hpp	100.0% <ø> (ø)
... and 56 more

... and 1 file with indirect coverage changes

[burgholzer]

That one cpp-linter failure cannot be fixed here since pybind11 is not available in the C++ linting environment.

[github-actions]

Cpp-Linter Report ⚠️

Some files did not pass the configured checks!

clang-tidy reports: 1 concern(s)

• include/mqt-core/python/pybind11.hpp

  include/mqt-core/python/pybind11.hpp:5:10: error: [clang-diagnostic-error]

  'pybind11/pybind11.h' file not found

  #include "pybind11/pybind11.h"
           ^~~~~~~~~~~~~~~~~~~~~

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