Add show method for QobjEvo

[ytdHuang]

Checklist

Thank you for contributing to QuantumToolbox.jl! Please make sure you have finished the following tasks before opening the PR.

• Please read Contributor Covenant Code of Conduct
• Any code changes were done in a way that does not break public API
• Appropriate tests were added and tested locally by running: make test.
• Any code changes should be julia formatted by running: make format.
• All documents (in docs/ folder) related to code changes were updated and able to build locally by running make docs.

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Description

This PR provides the show method for QobjEvo

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.81%. Comparing base (3357706) to head (b36d18c).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #272      +/-   ##
==========================================
- Coverage   94.39%   93.81%   -0.59%     
==========================================
  Files          32       32              
  Lines        2428     2426       -2     
==========================================
- Hits         2292     2276      -16     
- Misses        136      150      +14     

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