Modification on PERK time integrator to handle cases where s = e

[warisa-r]

If the user enters the number of stages 2 and 3 to PairedExplicitRK2 and PairedExplicitRK3, an error pops up since the integrator wasn't coded to handle the cases with no gamma to optimize. With this PR, this is handled. The bisect_stability_polynomial will return nothing, and dt_opt will be obtained from the bisection if the number of stages input by the user is equal to the consistency order of the time integration scheme.

Please let me know if you'd like anything changed!

[warisa-r]

@DanielDoehring

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 96.36%. Comparing base (62ff764) to head (78df3cc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ext/TrixiConvexECOSExt.jl	66.67%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2177      +/-   ##
==========================================
- Coverage   96.37%   96.36%   -0.00%     
==========================================
  Files         480      480              
  Lines       38225    38230       +5     
==========================================
+ Hits        36837    36840       +3     
- Misses       1388     1390       +2     

Flag	Coverage Δ
unittests	96.36% <89.47%> (-<0.01%)	⬇️

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[DanielDoehring]

Thanks for taking care of this so quick!