Fix backwards compatibility for union (#214)

In python 3.9 and below you can't do something like str | None in the
type definition of a function's arguments. However, this can be fixed by
using __future__.

Python stores the annotations as strings and doesn't try to evaluate
them. This allows you to write type hints using Python 3.10's syntax in
a Python 3.9 environment. When the code is actually run, the annotations
aren't evaluated, so there's no issue with the interpreter not
understanding the | operator for union types.

I checked and the | is only in this one file, elsewhere we are using Union. I replaced the | with Unions to make it consistent.

.changeset/five-lemons-join.md

@@ -0,0 +1,5 @@
+---
+"@e2b/python-sdk": patch
+---
+
+Fix Python 3.8 compatibility

packages/python-sdk/e2b/api/__init__.py

@@ -1,8 +1,10 @@
 from importlib.metadata import version
+from typing import Union
 
 from e2b.constants import API_HOST
 from e2b.api.metadata import default_headers
 
+
 pydantic_version = version("pydantic")
 if pydantic_version < "2.0.0":
     import e2b.api.v1.client as client
@@ -24,8 +26,8 @@
 class E2BApiClient(client.ApiClient):
     def __init__(
         self,
-        api_key: str | None = None,
-        access_token: str | None = None,
+        api_key: Union[str, None] = None,
+        access_token: Union[str, None] = None,
         *args,
         **kwargs,
     ):