Implementing TRestAxionMagneticFit and related classes

[jgalan]

• Implement a class TRestAxionMagneticFit that allows to describe the field along Z using a parametric function for each Bx, By, Bz component.

• Upgrade the TRestAxionMagneticFit and do the necessary changes so that we obtain a valid fit for any (X,Y) set values. Right now is optimized for X=340mm Y=0mm.

• Implement a new class TRestAxionMagnetModel that will contain the fits for all the (X,Y) values, and that defines an interpolation function to access the field on non-parallel tracks.

The following code can be used to reproduce the results obtained in this PR. Also found inside TRestAxionMagneticFit documentation.

TRestAxionMagneticField field("fields.rml", "babyIAXO_2024");

// Extracting the profile for each B-component (must be a parallel track)
Double_t dl = 50;
std::vector<Double_t> bX = field.GetComponentAlongPath( 0, TVector3(340, 0, -10000), TVector3(340, 0, 10000), dl );
std::vector<Double_t> bY = field.GetComponentAlongPath( 1, TVector3(340, 0, -10000), TVector3(340, 0, 10000), dl );
std::vector<Double_t> bZ = field.GetComponentAlongPath( 2, TVector3(340, 0, -10000), TVector3(340, 0, 10000), dl );
 
std::vector<Double_t> z;
for( int n = 0; n < bX.size(); n++ )
    z.push_back(dl/2 + n * dl);
 
TRestAxionMagneticFit bFit;
bFit.LoadData( z, bX, bY, bZ );
 
bFit.Fit( );
 
TCanvas *c = bFit.DrawComponents();
c->Print("bFit.png");

[jgalan]

Not needed anymore since @LouisHelary found a fix for the long computation times required on field retrieval at #92