support DP native model format

[njzjz]

Support framework-independent DP native model format as described in #2982. One can use dp convert-from -i frozen_model.pb -o frozen_model.dp and dp convert-from dp -i frozen_model.dp -o frozen_model.pb to convert between each other.

This PR supports:

• dp convert-from cli
• EnergyModel
• DescrptSeA
• EnerFitting

[codecov]

Codecov Report

Attention: 159 lines in your changes are missing coverage. Please review.

Comparison is base (f181a30) 75.90% compared to head (e12c10f) 75.51%.

Files	Patch %	Lines
deepmd/fit/fitting.py	32.60%	31 Missing ⚠️
deepmd/descriptor/se.py	19.35%	25 Missing ⚠️
deepmd/model/model.py	47.61%	22 Missing ⚠️
deepmd/utils/convert_dp.py	33.33%	20 Missing ⚠️
deepmd/fit/ener.py	20.83%	19 Missing ⚠️
deepmd/descriptor/se_a.py	25.00%	12 Missing ⚠️
deepmd/model/ener.py	29.41%	12 Missing ⚠️
deepmd/utils/type_embed.py	35.71%	9 Missing ⚠️
deepmd/entrypoints/convert.py	28.57%	5 Missing ⚠️
deepmd/descriptor/descriptor.py	42.85%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #2987      +/-   ##
==========================================
- Coverage   75.90%   75.51%   -0.40%     
==========================================
  Files         248      249       +1     
  Lines       25141    25357     +216     
  Branches     1598     1598              
==========================================
+ Hits        19084    19148      +64     
- Misses       5118     5270     +152     
  Partials      939      939              

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