add model compression support for models without training script

[denghuilu]

Add model compression support for models without training script. The main changes are:

• Allow users to provide the training script if there's no training script within the input frozen model.
• Note if there's a training script within the frozen model and the users provide one at the same time, the training script within the model will be used by default.

[codecov-commenter]

Codecov Report

Merging #948 (3479694) into devel (c4856ef) will decrease coverage by 7.85%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##            devel     #948      +/-   ##
==========================================
- Coverage   83.34%   75.49%   -7.86%     
==========================================
  Files         118       80      -38     
  Lines        9956     6770    -3186     
==========================================
- Hits         8298     5111    -3187     
- Misses       1658     1659       +1     

Impacted Files	Coverage Δ
deepmd/entrypoints/compress.py	80.76% <30.00%> (-10.35%)	⬇️
deepmd/entrypoints/train.py	87.19% <71.42%> (-0.78%)	⬇️
deepmd/entrypoints/main.py	88.42% <100.00%> (+0.12%)	⬆️
source/lib/tests/test_prod_force_a.cc
source/lib/tests/test_soft_min_switch_virial.cc
source/lib/tests/test_pair_tab.cc
source/lib/tests/test_prod_virial_grad_a.cc
source/lib/tests/test_prod_virial_r.cc
source/api_cc/tests/test_deeppolar.cc
source/api_cc/include/DataModifier.h
... and 31 more

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