Implemented OpenMP parallelization of the independent-transform loops in both files, following the existing #ifdef HAVE_GOMP / #pragma omp parallel for pattern already used elsewhere in the codebase:

- src/musrFT.cpp: the timed Transform() loop over all PFourier objects is now parallelized. Added OpenMP::OpenMP_CXX linkage to the musrFT CMake target (it wasn't linked before).
  - src/classes/PMusrCanvas.cpp (HandleFourier() and HandleDifferenceFourier()): split each loop into three phases — serial PFourier construction (FFTW plan creation isn't thread-safe), a parallel Transform()
    loop (pure FFTW compute, safe to parallelize), and serial ROOT histogram creation/styling (ROOT globals aren't thread-safe). PMusr already links OpenMP, so only the #include <omp.h> and the pragma were
    needed.

src/musrFT.cpp

@@ -31,6 +31,8 @@
 #include "config.h"
 #endif
 
+#include <omp.h>
+
 #include <sys/time.h>
 
 #include <iostream>
@@ -1463,7 +1465,14 @@ Int_t main(Int_t argc, Char_t *argv[])
     apodTag = F_APODIZATION_STRONG;
 
   Double_t start = millitime();
-  for (UInt_t i=0; i<fourier.size(); i++) {
+  Int_t noOfFourier = static_cast<Int_t>(fourier.size());
+  #ifdef HAVE_GOMP
+  Int_t chunk = noOfFourier/omp_get_num_procs();
+  if (chunk < 1)
+    chunk = 1;
+  #pragma omp parallel for default(shared) schedule(dynamic,chunk)
+  #endif
+  for (Int_t i=0; i<noOfFourier; i++) {
     fourier[i]->Transform(apodTag);
   }
   Double_t end = millitime();