Faster expansion of FunctionGenerator

[blegat]

This should make the GenOpt container then lowering with this bridge much faster than using JuMP.Container that expands the constraints at the JuMP level.

[codecov]

Codecov Report

❌ Patch coverage is 39.00293% with 208 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.06%. Comparing base (282362d) to head (98ca7a6).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bridge.jl	39.00%	208 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #15       +/-   ##
===========================================
- Coverage   64.77%   51.06%   -13.72%     
===========================================
  Files           6        6               
  Lines         318      656      +338     
===========================================
+ Hits          206      335      +129     
- Misses        112      321      +209     

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