fix: some issue of the output def

[wanghan-iapcm]

• strict type hint
• allow the last dim to be variable (by setting the dim to -1)
• remove variable def, which is not very useful.
• _derv_c should be defined for each atom (atomic virial)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1efc7f8) 76.22% compared to head (5b31c00) 76.22%.

Additional details and impacted files

@@           Coverage Diff           @@
##            devel    #3152   +/-   ##
=======================================
  Coverage   76.22%   76.22%           
=======================================
  Files         276      276           
  Lines       25631    25633    +2     
  Branches     1591     1591           
=======================================
+ Hits        19538    19540    +2     
  Misses       5162     5162           
  Partials      931      931           

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