Add __iter__ to TaxonomyIterator to satisfy Python iterator protocol

[audy]

Taxonomy doesn't have __iter__. This causes the following to break in IPython/Python REPL. I'm not sure why, but it doesn't fail if you run this in a script.

tax: taxonomy.Taxonomy

[ i for i in tax ] 

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[1], line 1
----> 1 [ i for i in build.taxonomy ]

TypeError: 'builtins.TaxonomyIterator' object is not iterable

The fix was to add __iter__

[pkonieczny]

👍