refactor: normalize ORB_ prefix filenames to lowercase (phase B)

Rename 18 files from ORB_* to orb_* (remove uppercase letters):
- ORB_atomic.{cpp,h} → orb_atomic.{cpp,h}
- ORB_atomic_lm.{cpp,h} → orb_atomic_lm.{cpp,h}
- ORB_gaunt_table.{cpp,h} → orb_gaunt_table.{cpp,h}
- ORB_nonlocal.{cpp,h} → orb_nonlocal.{cpp,h}
- ORB_nonlocal_lm.{cpp,h} → orb_nonlocal_lm.{cpp,h}
- ORB_read.{cpp,h} → orb_read.{cpp,h}
- ORB_{atomic_lm,nonlocal_lm,nonlocal,read}_test.cpp → orb_{...}_test.cpp
- ORB_unittest.{cpp,h} → orb_unittest.{cpp,h}

Update all #include references, CMakeLists.txt, Makefile.Objects,
and README. Class names, header guards, and CMake target identifiers
preserved unchanged.

Author: abacus_fixer

source/Makefile.Objects

@@ -432,12 +432,12 @@ OBJS_NEIGHBOR_SEARCH=neighbor_search.o\
     unitcell_lite.o\
 
 
-OBJS_ORBITAL=ORB_atomic.o\
-      ORB_atomic_lm.o\
-      ORB_gaunt_table.o\
-      ORB_nonlocal.o\
-      ORB_nonlocal_lm.o\
-      ORB_read.o\
+OBJS_ORBITAL=orb_atomic.o\
+      orb_atomic_lm.o\
+      orb_gaunt_table.o\
+      orb_nonlocal.o\
+      orb_nonlocal_lm.o\
+      orb_read.o\
       parallel_orbitals.o\
       atomic_radials.o\
       hydrogen_radials.o\

source/source_basis/module_ao/CMakeLists.txt

@@ -2,12 +2,12 @@ if(ENABLE_LCAO)
   add_library(
       orb
       OBJECT
-      ORB_atomic.cpp
-      ORB_atomic_lm.cpp
-      ORB_gaunt_table.cpp
-      ORB_nonlocal.cpp
-      ORB_nonlocal_lm.cpp
-      ORB_read.cpp
+      orb_atomic.cpp
+      orb_atomic_lm.cpp
+      orb_gaunt_table.cpp
+      orb_nonlocal.cpp
+      orb_nonlocal_lm.cpp
+      orb_read.cpp
       parallel_orbitals.cpp
       elem_basis_idx_orb.cpp
   )

source/source_basis/module_ao/README

@@ -20,18 +20,18 @@ Let me briefly describe the files contained in this 'ORB' module.
 --------------------------------------------------------------------
 ABACUS-ORB.x: the .exe file of the module
 main.cpp: main program file
-ORB_atomic.cpp: information for all of the atomic orbitals
-ORB_atomic.h
-ORB_atomic_lm.cpp: store each atomic orbitals
-ORB_atomic_lm.h
-ORB_gaunt_table.cpp: compute Gaunt tables
-ORB_gaunt_table.h
-ORB_nonlocal.cpp: information for all of the non-local projectors
-ORB_nonlocal.h
-ORB_nonlocal_lm.cpp: store each non-local projector
-ORB_nonlocal_lm.h
-ORB_read.cpp: read-in basis sets/non-local projectors/descriptors
-ORB_read.h
+orb_atomic.cpp: information for all of the atomic orbitals
+orb_atomic.h
+orb_atomic_lm.cpp: store each atomic orbitals
+orb_atomic_lm.h
+orb_gaunt_table.cpp: compute Gaunt tables
+orb_gaunt_table.h
+orb_nonlocal.cpp: information for all of the non-local projectors
+orb_nonlocal.h
+orb_nonlocal_lm.cpp: store each non-local projector
+orb_nonlocal_lm.h
+orb_read.cpp: read-in basis sets/non-local projectors/descriptors
+orb_read.h
 --------------------------------------------------------------------
 
 There are some other files in the 'OBJS_BASE' group (mainly math functions), 

source/source_basis/module_ao/elem_basis_idx_orb.cpp

@@ -1,7 +1,7 @@
 #include "elem_basis_idx_orb.h"
 
-#include "ORB_read.h"
-#include "ORB_atomic_lm.h"
+#include "orb_read.h"
+#include "orb_atomic_lm.h"
 
 namespace ModuleBase
 {

source/source_basis/module_ao/orb_atomic.cpp

@@ -1,4 +1,4 @@
-#include "ORB_atomic.h"
+#include "orb_atomic.h"
 
 Numerical_Orbital_AtomRelation Numerical_Orbital::NOAR;
 

source/source_basis/module_ao/orb_atomic.h

@@ -5,7 +5,7 @@
 
 #include "source_base/intarray.h"
 #include "source_base/vector3.h"
-#include "ORB_atomic_lm.h"
+#include "orb_atomic_lm.h"
 
 class Numerical_Orbital_AtomRelation
 {

source/source_basis/module_ao/orb_atomic_lm.cpp

@@ -1,4 +1,4 @@
-#include "ORB_atomic_lm.h"
+#include "orb_atomic_lm.h"
 #include "source_base/sph_bessel_recursive.h"
 #include "source_base/global_variable.h"
 #include "source_base/tool_quit.h"

source/source_basis/module_ao/orb_gaunt_table.cpp

@@ -1,6 +1,6 @@
 #include <math.h>
 #include <cassert>
-#include "ORB_gaunt_table.h"
+#include "orb_gaunt_table.h"
 #include "source_base/timer.h"
 #include "source_base/memory_recorder.h"
 #include "source_base/mathzone.h"

source/source_basis/module_ao/orb_nonlocal.cpp

@@ -1,4 +1,4 @@
-#include "ORB_nonlocal.h"
+#include "orb_nonlocal.h"
 #include "source_base/global_function.h"
 
 Numerical_Nonlocal::Numerical_Nonlocal()

source/source_basis/module_ao/orb_nonlocal.h

@@ -2,7 +2,7 @@
 #define NUMERICAL_NONLOCAL_H
 
 #include "source_base/complexmatrix.h"
-#include "ORB_nonlocal_lm.h"
+#include "orb_nonlocal_lm.h"
 /**
  * \class Numerical_Nonlocal
  *CLASS  Numerical_Nonlocal