Improve PR #1174 (Reduce time spent in eval and der in equation resolution)

[SylvestreSakti]

What kind of change does this PR introduce?
Optimization propsoed to improve PR #1174 (these modifications aims at being merged on the corresponding branch)

3 main improvements proposed :

• Do not compute again sin(ksi), cos(ksi), theta1 and theta2, and store them in double arrays (to compute them only once for both eval and der)
• Do not search for Variable.getRow() while filling the matrix for der() but store the rows in arrays before
• Do not check active status of EquationTerm and Equation while computing eval and der but just store active status of both in one array (named termToDer and termToEval)

-> Tested for some country networks : this improves 4 to 5 % time spent to compute an AC Security Analysis

[vidaldid-rte]

Nothing wrong with your PR.
But I realise that those field may depend on the tap for transformers with tap changer capabilities.
The fields are final in the main branch.
But it seems their is a bug here. They should be updated when a tap changes. Maybe to handle in a separate PR...
That wille be easier once we have centralized them.

[sonarqubecloud]

Quality Gate passed

Issues
8 New issues
0 Accepted issues

Measures
0 Security Hotspots
98.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud