insert license to C++ header files

[njzjz]

Follow up #2639.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.05 ⚠️

Comparison is base (533745a) 78.35% compared to head (979db59) 78.31%.

❗ Current head 979db59 differs from pull request most recent head 7aa2e0f. Consider uploading reports for the commit 7aa2e0f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #2652      +/-   ##
==========================================
- Coverage   78.35%   78.31%   -0.05%     
==========================================
  Files         235      235              
  Lines       24474    24473       -1     
  Branches     1469     1469              
==========================================
- Hits        19177    19165      -12     
- Misses       4907     4918      +11     
  Partials      390      390              

Impacted Files	Coverage Δ
source/api_c/include/deepmd.hpp	85.69% <ø> (ø)
source/api_cc/include/AtomMap.h	100.00% <ø> (ø)
source/api_cc/include/DataModifier.h	28.57% <ø> (ø)
source/api_cc/include/DeepPot.h	95.23% <ø> (-0.22%)	⬇️
source/api_cc/include/DeepTensor.h	87.50% <ø> (ø)
source/api_cc/include/common.h	100.00% <ø> (ø)
source/ipi/include/Convert.h	100.00% <ø> (ø)
source/ipi/include/StringSplit.h	100.00% <ø> (ø)
source/lib/include/ComputeDescriptor.h	91.08% <ø> (ø)
source/lib/include/SimulationRegion.h	50.00% <ø> (ø)
... and 11 more

... and 2 files with indirect coverage changes

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