Fix Bloch docstrings and improve visualization of the sphere

[ytdHuang]

Checklist

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

• Please read Contributing to Quantum Toolbox in Julia.
• 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.
• (If necessary) the CHANGELOG.md should be updated (regarding to the code changes) and built by running: make changelog.

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Description

This PR does:

• set default font size to 20
• add kwargs kind for add_states! (same as qutip)
• improve the handling of plot vector arrow length.
• fix all incorrect docstrings
• merge the codes in _draw_reference_circles! and _draw_axes! into _draw_bloch_sphere!
• remove redundant wire frame drawings

[codecov]

Codecov Report

Attention: Patch coverage is 98.03922% with 1 line in your changes missing coverage. Please review.

Project coverage is 94.06%. Comparing base (22efb11) to head (9e7d544).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/visualization.jl	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
+ Coverage   93.97%   94.06%   +0.08%     
==========================================
  Files          50       50              
  Lines        3418     3418              
==========================================
+ Hits         3212     3215       +3     
+ Misses        206      203       -3     

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