➖ only require typing_extensions on Python < 3.11

[burgholzer]

Description

This PR removes the typing_extensions dependency for Python >= 3.11 and adds a compatibility typing module to abstract away the difference across Python versions.

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 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 95.4%. Comparing base (1ae653b) to head (b30b25a).
Report is 81 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mqt/qcec/_compat/typing.py	0.0%	8 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #445     +/-   ##
=======================================
- Coverage   95.8%   95.4%   -0.5%     
=======================================
  Files         39      40      +1     
  Lines       1831    1839      +8     
  Branches     224     224             
=======================================
  Hits        1755    1755             
- Misses        76      84      +8     

Flag	Coverage Δ		*Carryforward flag
cpp	95.8% <ø> (ø)		Carriedforward from 1ae653b
python	94.0% <0.0%> (-1.9%)	⬇️

*This pull request uses carry forward flags. Click here to find out more.

Files with missing lines	Coverage Δ
src/mqt/qcec/verify.py	100.0% <ø> (ø)
src/mqt/qcec/verify_compilation_flow.py	100.0% <ø> (ø)
src/mqt/qcec/_compat/typing.py	0.0% <0.0%> (ø)