modified PTDF functions for Dense method

[alefcastelli]

Modified methods for the Dense method. Significant improvements in computational time were recorded

[github-actions]

Performance Results

Version	Precompile Time
Main	2.547323677
This Branch	2.590044415

Version	Execute Time
Main-Build PTDF First	5.131222607
Main-Build PTDF Second	0.126453405
Main-Build Ybus First	0.424831178
Main-Build Ybus Second	0.010313635
Main-Build LODF First	0.605555054
Main-Build LODF Second	0.260098748
This Branch-Build PTDF First	5.640806902
This Branch-Build PTDF Second	0.160099344
This Branch-Build Ybus First	0.425639845
This Branch-Build Ybus Second	0.00946495
This Branch-Build LODF First	0.558417946
This Branch-Build LODF Second	0.254845944

[codecov]

Codecov Report

Merging #58 (8ae8a0d) into main (14ad47f) will increase coverage by 0.23%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #58      +/-   ##
==========================================
+ Coverage   78.14%   78.37%   +0.23%     
==========================================
  Files          14       14              
  Lines        1130     1119      -11     
==========================================
- Hits          883      877       -6     
+ Misses        247      242       -5     

Flag	Coverage Δ
unittests	78.37% <100.00%> (+0.23%)	⬆️

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

Files Changed	Coverage Δ
src/ptdf_calculations.jl	94.70% <100.00%> (+2.77%)	⬆️

... and 1 file with indirect coverage changes