[Fix]: Check convergence in NLSolver before returning solution

[Ady0333]

Summary

Fixes #1282

When nlsolve() fails to converge, NLSolver now checks the convergence status before returning the solution. Previously, it silently copied the unconverged last iterate.

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Changes

• src/Algebra/NLSolvers.jl: Add converged() check after nlsolve() call
• src/ODEs/StageOperators.jl: Same fix for ODE/transient context

---

Behavior

Before: Unconverged Newton iterates silently returned as valid solutions
After: Throws error with iteration count and residual norm

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Testing

Tested with a nonlinear problem that fails to converge:

• Previously: returned x=44.44 (wrong) with no error
• Now: throws "Newton solver did not converge after 5 iterations. Final residual norm: 87788"

All existing Gridap tests pass.

[Ady0333]

Hello @JordiManyer and @oriolcg!!! Please review this pr and let me know if any changes are needed...

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.82%. Comparing base (d6858fa) to head (77a9ed7).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Algebra/NLSolvers.jl	50.00%	1 Missing ⚠️
src/ODEs/StageOperators.jl	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1283      +/-   ##
==========================================
- Coverage   88.83%   88.82%   -0.01%     
==========================================
  Files         227      227              
  Lines       29749    29753       +4     
==========================================
+ Hits        26427    26429       +2     
- Misses       3322     3324       +2     

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[JordiManyer]

Thanks @Ady0333 for the contribution, I don't see any issue with the PR. Could you please update NEWS.md with the changes? Cheers!

[Ady0333]

Thanks @Ady0333 for the contribution, I don't see any issue with the PR. Could you please update NEWS.md with the changes? Cheers!

Thanks for the review...I have updated the NEWS.md file.