Read/write problems to JSON files

[goulart-paul]

Adds a "serde" option enabling read/write of problem data to a JSON file. The output to this file will be the unscaled problem data and settings, but written after any presolve or chordal decomposition steps are applied. To get an exact copy of what the solver first received, it is necessary to disable those options before writing.

Implements wrappers for these read/write functions in both the internal ClarabelRs julia wrapper and for the python wrappers.

[codecov]

Codecov Report

Attention: Patch coverage is 97.43590% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 87.30%. Comparing base (192fa0b) to head (6734765).
Report is 3 commits behind head on main.

Files	Patch %	Lines
src/solver/implementations/default/json.rs	97.43%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #111      +/-   ##
==========================================
+ Coverage   86.56%   87.30%   +0.74%     
==========================================
  Files          78       76       -2     
  Lines        6058     6050       -8     
==========================================
+ Hits         5244     5282      +38     
+ Misses        814      768      -46     

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