Remove Re-export

[albertomercurio]

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

Here we remove the Reexport dependency, as well as reorganizing the functions to be re-exported.

More specifically, we try to re-export external functions as less as possible.

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.36%. Comparing base (6898156) to head (64d0c87).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/qobj/dimensions.jl	66.66%	1 Missing ⚠️
src/utilities.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #443      +/-   ##
==========================================
- Coverage   94.39%   94.36%   -0.04%     
==========================================
  Files          47       47              
  Lines        2997     2997              
==========================================
- Hits         2829     2828       -1     
- Misses        168      169       +1     

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