fix incorrect type hints and docstrings

[njzjz]

For example, Return should be Returns... See style guide.

[codecov-commenter]

Codecov Report

Merging #1001 (8ba1352) into devel (f2a7303) will decrease coverage by 11.17%.
The diff coverage is n/a.

❗ Current head 8ba1352 differs from pull request most recent head 9acd269. Consider uploading reports for the commit 9acd269 to get more accurate results

@@             Coverage Diff             @@
##            devel    #1001       +/-   ##
===========================================
- Coverage   75.46%   64.28%   -11.18%     
===========================================
  Files          85        5       -80     
  Lines        6794       14     -6780     
===========================================
- Hits         5127        9     -5118     
+ Misses       1667        5     -1662     

Impacted Files	Coverage Δ
deepmd/infer/__init__.py
deepmd/__init__.py
source/op/_prod_virial_grad.py
deepmd/descriptor/se_a_ebd.py
deepmd/utils/sess.py
deepmd/entrypoints/config.py
deepmd/infer/deep_wfc.py
deepmd/utils/convert.py
source/op/_soft_min_force_grad.py
source/op/_prod_force_se_a_grad.py
... and 51 more

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