📝 Add documentation for DD package

[burgholzer]

Description

This pull request includes extensive documentation updates for the DD package C++ module of MQT Core.

Fixes #814

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

Attention: Patch coverage is 95.45455% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.3%. Comparing base (092f88a) to head (4208b2a).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dd/FunctionalityConstruction.cpp	82.3%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #831     +/-   ##
=======================================
- Coverage   92.3%   92.3%   -0.1%     
=======================================
  Files        127     127             
  Lines      13509   13544     +35     
  Branches    2080    2085      +5     
=======================================
+ Hits       12476   12506     +30     
- Misses      1033    1038      +5     

Flag	Coverage Δ
cpp	92.0% <95.4%> (-0.1%)	⬇️
python	99.7% <ø> (ø)

Files with missing lines	Coverage Δ
include/mqt-core/dd/CachedEdge.hpp	84.2% <ø> (ø)
include/mqt-core/dd/Complex.hpp	100.0% <ø> (ø)
include/mqt-core/dd/ComplexValue.hpp	87.5% <ø> (ø)
include/mqt-core/dd/ComputeTable.hpp	100.0% <100.0%> (ø)
include/mqt-core/dd/Edge.hpp	94.1% <ø> (ø)
include/mqt-core/dd/Operations.hpp	75.5% <100.0%> (ø)
include/mqt-core/dd/Package.hpp	96.3% <100.0%> (-0.4%)	⬇️
include/mqt-core/dd/Simulation.hpp	100.0% <ø> (ø)
include/mqt-core/dd/UnaryComputeTable.hpp	92.0% <100.0%> (-0.6%)	⬇️
src/dd/Simulation.cpp	93.4% <100.0%> (ø)
... and 1 more