📝 Prepare docs for new release

[burgholzer]

Description

This PR just fixes up a couple of things throughout the documentation regarding the move from qecc to mqt-qecc and from the QFR library to MQT Core. It also slightly updates the RtD documentation to bring it more in line with QCEC and QMAP.

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 #156 (c3660d4) into main (a7791a5) will decrease coverage by 0.2%. The diff coverage is n/a.

@@           Coverage Diff           @@
##            main    #156     +/-   ##
=======================================
- Coverage   85.7%   85.6%   -0.2%     
=======================================
  Files         20      20             
  Lines       1362    1362             
  Branches     190     190             
=======================================
- Hits        1168    1166      -2     
- Misses       194     196      +2     

Flag	Coverage Δ
cpp	79.5% <ø> (-0.3%)	:arrow_down:
python	97.2% <ø> (ø)

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see 1 file with indirect coverage changes