Resolve type instabilities while generating Qobj (2nd try)

[ytdHuang]

This is the second try for PR #178, and also fixes #177.

Summary of this PR:

• Add type instability tests
• Gather some of the Error tests together in QuantumObject testset

When the input array is a matrix, and the user didn't specify type. We test this kind of cases with the following code:

T = ComplexF64
UnionType = Union{QuantumObject{Matrix{T},BraQuantumObject},QuantumObject{Matrix{T},OperatorQuantumObject}}
a = rand(T, 1, 10)
@inferred UnionType Qobj(a)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.37%. Comparing base (4f94f9b) to head (be9da54).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
+ Coverage   93.35%   93.37%   +0.01%     
==========================================
  Files          28       28              
  Lines        2093     2098       +5     
==========================================
+ Hits         1954     1959       +5     
  Misses        139      139              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.