Disable NaN sanity check in bssn_rhs.f90 for production builds

Wrap the NaN sanity check (21 sum() full-array traversals per RHS call)
with #ifdef DEBUG so it is compiled out in production builds.

This eliminates 84 redundant full-array scans per timestep (21 per RHS
call × 4 RK4 substages) that serve no purpose when input data is valid.

Usage:
  - Production build (default): NaN check is disabled, no changes needed.
  - Debug build: add -DDEBUG to f90appflags in makefile.inc, e.g.
      f90appflags = -O3 ... -DDEBUG -fpp ...
    to re-enable the NaN sanity check.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

AMSS_NCKU_source/bssn_rhs.f90

@@ -106,7 +106,8 @@
   call getpbh(BHN,Porg,Mass)
 #endif
 
-!!! sanity check
+!!! sanity check (disabled in production builds for performance)
+#ifdef DEBUG
   dX = sum(chi)+sum(trK)+sum(dxx)+sum(gxy)+sum(gxz)+sum(dyy)+sum(gyz)+sum(dzz) &
       +sum(Axx)+sum(Axy)+sum(Axz)+sum(Ayy)+sum(Ayz)+sum(Azz)                   &
       +sum(Gamx)+sum(Gamy)+sum(Gamz)                                           &
@@ -136,6 +137,7 @@
      gont = 1
      return
   endif
+#endif
 
   PI = dacos(-ONE)