docs: add documentation of each attributes of is and as

[lambdalisue]

Close #90

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.18%. Comparing base (06da9f8) to head (4900dad).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #106      +/-   ##
==========================================
+ Coverage   97.98%   98.18%   +0.19%     
==========================================
  Files          50       50              
  Lines         794      880      +86     
  Branches       85       85              
==========================================
+ Hits          778      864      +86     
  Misses         16       16              

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[lambdalisue]

https://jsr.io/@core/unknownutil@4.0.3-pre.0/doc/~/as

Unfortunately, it seems generation doesn't help the situation 😢