Cannot pickle `preprocessing.OrdinalEncoder` instance

[Bing-su]

river version: 0.22.0
Python version: 3.10.12 (google colab)
Operating system: Linux (google colab)

Describe the bug

Cannot pickle preprocessing.OrdinalEncoder instance

Steps/code to reproduce

import pickle

from river import preprocessing

X = [
    {"country": "France", "place": "Taco Bell"},
    {"country": None, "place": None},
    {"country": "Sweden", "place": "Burger King"},
    {"country": "France", "place": "Burger King"},
    {"country": "Russia", "place": "Starbucks"},
    {"country": "Russia", "place": "Starbucks"},
    {"country": "Sweden", "place": "Taco Bell"},
    {"country": None, "place": None},
]

encoder = preprocessing.OrdinalEncoder()
for x in X:
    print(encoder.transform_one(x))
    encoder.learn_one(x)

with open("encoder.pkl", "wb") as f:
    pickle.dump(encoder, f)

{'country': 0, 'place': 0}
{'country': -1, 'place': -1}
{'country': 0, 'place': 0}
{'country': 1, 'place': 2}
{'country': 0, 'place': 0}
{'country': 3, 'place': 3}
{'country': 2, 'place': 1}
{'country': -1, 'place': -1}

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

[<ipython-input-3-fa4773e7a2b5>](https://localhost:8080/#) in <cell line: 21>()
     20 
     21 with open("encoder.pkl", "wb") as f:
---> 22     pickle.dump(encoder, f)

TypeError: cannot pickle 'generator' object

The problematic generator seems to be this one.

river/river/preprocessing/ordinal.py

Lines 13 to 14 in 5531ae5

	def make_counter(skip):
	return (i for i in itertools.count() if i not in skip)

[MaxHalford]

Good catch!