Updates for JuMP's New NL Interface

[ccoffrin]

Remove @NL macros and simplify code that branched on NL vs non-NL models.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (a2856d1) 93.98% compared to head (8cea192) 94.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #901      +/-   ##
==========================================
+ Coverage   93.98%   94.22%   +0.24%     
==========================================
  Files          43       43              
  Lines        9637     9612      -25     
==========================================
  Hits         9057     9057              
+ Misses        580      555      -25     

Files	Coverage Δ
src/form/acp.jl	93.23% <100.00%> (-0.48%)	⬇️
src/form/acr.jl	98.47% <100.00%> (-0.04%)	⬇️
src/form/act.jl	95.00% <100.00%> (ø)
src/form/iv.jl	92.66% <100.00%> (ø)
src/core/objective.jl	95.90% <87.50%> (+0.11%)	⬆️

... and 16 files with indirect coverage changes

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[odow]

LGTM

[ccoffrin]

I am going to hold merging and tagging for about a week to see if there is any feedback from other package developers.

[ccoffrin]

@odow, FYI on this weird Ipopt behavior on Windows in Julia v1.6, https://github.com/lanl-ansi/PowerModels.jl/actions/runs/7587175654/job/20666919070