📝 Prepare docs for new release

[burgholzer]

Description

This PR just fixes up a couple of things throughout the documentation regarding the move from qcec to mqt-qcec and from the QFR library to MQT Core.

Checklist:

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

[codecov[bot]]

Codecov Report

Merging #299 (62027a8) into main (3ccd518) will not change coverage. The diff coverage is n/a.

@@          Coverage Diff          @@
##            main    #299   +/-   ##
=====================================
  Coverage   96.1%   96.1%           
=====================================
  Files         34      34           
  Lines       1720    1720           
  Branches     208     208           
=====================================
  Hits        1653    1653           
  Misses        67      67           

Flag	Coverage Δ
cpp	95.7% <ø> (ø)
python	97.1% <ø> (ø)

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