Implement a function to calculate the optimal CFL number for the PERK2 integrator and apply the necessary related updates

[warisa-r]

This PR introduces a new function to compute the optimal CFL number based on the optimal time step for the PairedExplicitRK2 (PERK2) integrator.

• Added dt_opt as a new attribute of PairedExplicitRK2 to store the optimal time step.
• Modified the constructor of PairedExplicitRK2 that takes in the file path of the monomial coefficients to include an extra argument dt_opt, which is a breaking change Release v0.9 #1997.
• Implemented calculate_cfl function to compute the CFL number from the optimal time step.
• Created a new example demonstrating how to use the calculate_cfl function with the PERK2 integrator.
• Added a test to validate the new example showing the usage of the calculate_cfl function with the PERK2 integrator.

Please let me know if there are any suggestions or improvements!
Original PR: #2077

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.34%. Comparing base (da287ef) to head (452b132).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2083      +/-   ##
==========================================
+ Coverage   96.32%   96.34%   +0.02%     
==========================================
  Files         470      470              
  Lines       37492    37501       +9     
==========================================
+ Hits        36114    36129      +15     
+ Misses       1378     1372       -6     

Flag	Coverage Δ
unittests	96.34% <100.00%> (+0.02%)	⬆️

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[DanielDoehring]

Re-opens #2077.

[sloede]

Please let us know once ready for review 🙂

[DanielDoehring]

Please let us know once ready for review 🙂

Feel free to drop any comment, this is good to go (was already good to go 😅😬) from my side.

[ranocha]

This is a breaking change, @sloede. Do you want to handle the breaking release right now?