Replace Fortran bssn_rhs with C implementation and add C helper kernels

- Modify bssn_rhs_c.C to use existing project headers (macrodef.h, bssn_rhs.h)
- Update makefile: remove bssn_rhs.o from F90FILES, add CFILES with OpenMP
- Keep Fortran helper files (diff_new.f90, kodiss.f90, lopsidediff.f90) for other Fortran callers

[copilot: fix compiling errors & a nan error]

Co-authored-by: ianchb <i@4t.pw>
Co-authored-by: copilot-swe-agent[bot] <198982749+copilot@users.noreply.github.com>

AMSS_NCKU_source/tool.h

@@ -0,0 +1,27 @@
+#include "share_func.h"
+void fdderivs(const int ex[3],
+              const double *f,
+              double *fxx, double *fxy, double *fxz,
+              double *fyy, double *fyz, double *fzz,
+              const double *X, const double *Y, const double *Z,
+              double SYM1, double SYM2, double SYM3,
+              int Symmetry, int onoff);
+
+void fderivs(const int ex[3],
+             const double *f,
+             double *fx, double *fy, double *fz,
+             const double *X, const double *Y, const double *Z,
+             double SYM1, double SYM2, double SYM3,
+             int Symmetry, int onoff);
+
+void kodis(const int ex[3],
+           const double *X, const double *Y, const double *Z,
+           const double *f, double *f_rhs,
+           const double SoA[3],
+           int Symmetry, double eps);
+
+void lopsided(const int ex[3],
+              const double *X, const double *Y, const double *Z,
+              const double *f, double *f_rhs,
+              const double *Sfx, const double *Sfy, const double *Sfz,
+              int Symmetry, const double SoA[3]);