Change show(::IO, ::GenericModel) to a more informative tree structure

[odow]

Closes #3802

• https://github.com/jump-dev/JuMP.jl/actions/runs/10313637410

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.90%. Comparing base (23ccb2c) to head (f7dce00).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3803      +/-   ##
==========================================
- Coverage   98.40%   97.90%   -0.51%     
==========================================
  Files          44       44              
  Lines        5968     6010      +42     
==========================================
+ Hits         5873     5884      +11     
- Misses         95      126      +31     

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[blegat]

Much better, I like it

[odow]

@pulsipher this breaks a printing test in InfiniteOpt. Thoughts?

[pulsipher]

@pulsipher this breaks a printing test in InfiniteOpt. Thoughts?

This is not unexpected and I think this is a good PR. I can update InfiniteOpt once this PR is merged and make that particular test more robust printing changes in JuMP when I am at it.