Add tests for Python 3.9

[jamescalam]

Heard from users that there are issues when running with py3.9 — we should add tests and adjust if required.

[rhamnett]

Hi @jamescalam the issue is with the pipe (OR operator):

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[1], line 1
----> 1 from semantic_router import Route
      3 # we could use this as a guide for our chatbot to avoid political conversations
      4 politics = Route(
      5     name="politics",
      6     utterances=[
   (...)
     12     ],
     13 )

File ~/anaconda3/envs/pytorch_and_rapids/lib/python3.9/site-packages/semantic_router/__init__.py:1
----> 1 from semantic_router.hybrid_layer import HybridRouteLayer
      2 from semantic_router.layer import RouteLayer, LayerConfig
      3 from semantic_router.route import Route

File ~/anaconda3/envs/pytorch_and_rapids/lib/python3.9/site-packages/semantic_router/hybrid_layer.py:4
      1 import numpy as np
      2 from numpy.linalg import norm
----> 4 from semantic_router.encoders import (
      5     BaseEncoder,
      6     BM25Encoder,
      7     CohereEncoder,
      8     OpenAIEncoder,
      9 )
     10 from semantic_router.utils.logger import logger
     12 from semantic_router.route import Route

File ~/anaconda3/envs/pytorch_and_rapids/lib/python3.9/site-packages/semantic_router/encoders/__init__.py:2
      1 from semantic_router.encoders.base import BaseEncoder
----> 2 from semantic_router.encoders.bm25 import BM25Encoder
      3 from semantic_router.encoders.cohere import CohereEncoder
      4 from semantic_router.encoders.openai import OpenAIEncoder

File ~/anaconda3/envs/pytorch_and_rapids/lib/python3.9/site-packages/semantic_router/encoders/bm25.py:8
      3 from pinecone_text.sparse import BM25Encoder as encoder
      5 from semantic_router.encoders import BaseEncoder
----> 8 class BM25Encoder(BaseEncoder):
      9     model: Any | None = None
     10     idx_mapping: dict[int, int] | None = None

File ~/anaconda3/envs/pytorch_and_rapids/lib/python3.9/site-packages/semantic_router/encoders/bm25.py:9, in BM25Encoder()
      8 class BM25Encoder(BaseEncoder):
----> 9     model: Any | None = None
     10     idx_mapping: dict[int, int] | None = None
     11     type: str = "sparse"

TypeError: unsupported operand type(s) for |: '_SpecialForm' and 'NoneType'