add sub_kwargs parameter to LMSolver and solve! for subsolver

[MohamedLaghdafHABIBOULLAH]

As discussed in Zulip this might reduce considerably the number of inner prox as for R2N and TR @dpo @MaxenceGollier

[Copilot]

Pull Request Overview

This PR adds a sub_kwargs parameter to the LMSolver to allow passing custom keyword arguments to the subsolver, which can help reduce the number of inner proximal iterations for solvers like R2N and TR.

• Adds sub_kwargs parameter to both the documentation and function signature
• Updates subsolver calls to include the new keyword arguments via splatting

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.68%. Comparing base (e0f214d) to head (80f981f).
⚠️ Report is 247 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #245       +/-   ##
===========================================
+ Coverage   61.53%   84.68%   +23.15%     
===========================================
  Files          11       13        +2     
  Lines        1292     1626      +334     
===========================================
+ Hits          795     1377      +582     
+ Misses        497      249      -248     

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[MohamedLaghdafHABIBOULLAH]

Thanks @MaxenceGollier