Migrate to Jupyter Notebook version 7

[m-rossi]

New feature/Bug fix description

Jupyter Notebook version 7 changed quite a lot under the hood and a few adjustments are needed in jupyter-docx-bundler

Related issues

Close #99

Checklist

• Tests have passed
• New code is covered with tests

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.02% ⚠️

Comparison is base (8519db2) 97.22% compared to head (8425d83) 97.21%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #100      +/-   ##
==========================================
- Coverage   97.22%   97.21%   -0.02%     
==========================================
  Files           6        6              
  Lines         540      502      -38     
==========================================
- Hits          525      488      -37     
+ Misses         15       14       -1     

Files Changed	Coverage Δ
jupyter_docx_bundler/__init__.py	100.00% <ø> (+4.16%)	⬆️
jupyter_docx_bundler/tests/test_bundler.py	100.00% <ø> (ø)
jupyter_docx_bundler/tests/test_converters.py	100.00% <100.00%> (ø)

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