Fix incorrect inputs for functions that generate states

[ytdHuang]

close #154

Summary for this PR:

• fock can only return Ket
• basis can only return Ket
• rand_dm can only return Operator
• users can specify the keyword argument dims for all the functions above, and will check whether the arguments are correct by directly passing them to QuantumObject(A; type = type, dims = dims)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.52%. Comparing base (c6e8b56) to head (0825a97).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
+ Coverage   92.47%   92.52%   +0.05%     
==========================================
  Files          26       26              
  Lines        1847     1847              
==========================================
+ Hits         1708     1709       +1     
+ Misses        139      138       -1     

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