🔥 drop Python 3.8 support

[burgholzer]

Description

Python 3.8 will reach end of live in October 2024.
Qiskit is already issuing deprecation warnings since a couple of releases when using it on Python 3.8.
This PR officially drops support for Python 3.8 in mqt-qmap.

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 ✅

Project coverage is 90.6%. Comparing base (4d430cb) to head (bf8a6c6).
Report is 172 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #515     +/-   ##
=======================================
+ Coverage   90.4%   90.6%   +0.1%     
=======================================
  Files         87      87             
  Lines      10050   10046      -4     
  Branches    1716    1716             
=======================================
+ Hits        9090    9102     +12     
+ Misses       960     944     -16     

Flag	Coverage Δ
cpp	90.3% <ø> (+0.1%)	⬆️
python	95.9% <100.0%> (ø)

Files with missing lines	Coverage Δ
src/mqt/qmap/subarchitectures.py	95.4% <100.0%> (ø)

... and 3 files with indirect coverage changes