Add support for get MOI.NLPBlock

[odow]

@ccoffrin you can replace
https://github.com/lanl-ansi/rosetta-opf/blob/1867107cb8b2d036dcd7ddac13637f627dd84ab5/jump.jl#L119C5-L119C55
with

nlp_block = unsafe_backend(model).nlp_data

but once this is merged you'll be able to use

nlp_block = JuMP.MOI.get(unsafe_backend(model), JuMP.MOI.NLPBlock())

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (04178d8) 94.22% compared to head (e0155d0) 94.25%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #398      +/-   ##
==========================================
+ Coverage   94.22%   94.25%   +0.02%     
==========================================
  Files           4        4              
  Lines         953      957       +4     
==========================================
+ Hits          898      902       +4     
  Misses         55       55              

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