Jd/thermal modeling changes

[jd-lara]

This PR fixes some loops in ThermalMultiStart and also uses nothing for LB on variables for UC. The rationale for this is that in some cases thermal units with negative limits are being used to represent transactions with other areas where the power is negative. This is a work around while we implement a more rigorous way to do inter-regional transactions.

[github-actions]

Performance Results

Version	Precompile Time
Main	3.285255294
This Branch	3.22066535

Version	Build Time
Main-Build Time Precompile	50.807528699
Main-Build Time Postcompile	2.599317277
This Branch-Build Time Precompile	51.207137836
This Branch-Build Time Postcompile	2.753019327

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (1c05b65) 80.51% compared to head (901573e) 80.52%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1059   +/-   ##
=======================================
  Coverage   80.51%   80.52%           
=======================================
  Files         115      115           
  Lines       12395    12396    +1     
=======================================
+ Hits         9980     9982    +2     
+ Misses       2415     2414    -1     

Flag	Coverage Δ
unittests	80.52% <63.63%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/devices_models/devices/AC_branches.jl	76.95% <100.00%> (-0.11%)	⬇️
src/devices_models/devices/thermal_generation.jl	90.15% <61.90%> (-0.29%)	⬇️

... and 1 file with indirect coverage changes