fix: Fix implicit imports in notebooks

[mark-koch]

Fixes #490

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.86207% with 7 lines in your changes missing coverage. Please review.

Project coverage is 91.41%. Comparing base (f24183d) to head (f9aaaa9).

Files with missing lines	Patch %	Lines
guppylang/ipython_inspect.py	33.33%	4 Missing ⚠️
guppylang/decorator.py	86.95%	3 Missing ⚠️

Additional details and impacted files

@@                     Coverage Diff                      @@
##           feat/implicit-decorators     #495      +/-   ##
============================================================
- Coverage                     91.51%   91.41%   -0.10%     
============================================================
  Files                            59       59              
  Lines                          6044     6059      +15     
============================================================
+ Hits                           5531     5539       +8     
- Misses                          513      520       +7     

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