Refactor&Test: Share RT-TDDFT velocity gauge projector snap integration and add unit test (deepmodeling#7539)

* Refactor: Share RT-TDDFT projector snap integration

* Docs: Comment RT-TDDFT projector snap integration

Author: AsTonyshment

source/source_lcao/module_rt/CMakeLists.txt

@@ -12,6 +12,7 @@ if(ENABLE_LCAO)
         upsi.cpp
         td_info.cpp
         velocity_op.cpp
+        snap_projector_half_tddft.cpp
         snap_psibeta_half_tddft.cpp
         td_folding.cpp
         solve_propagation.cpp