Update base.py to remove setuptools and use standard library

[justinpolygon]

This PR updates the method for retrieving the version number of the polygon-api-client package. It replaces the use of pkg_resources from setuptools with importlib.metadata, which is part of the standard library in Python 3.8 and newer.

Changes

• Removed import pkg_resources and replaced it with from importlib.metadata import version, PackageNotFoundError.
• Updated the version retrieval logic to use importlib.metadata.version instead of pkg_resources.require.

Benefits

• Reduces external dependency on setuptools which is deprecated and causing issues (pkg_resources is deprecated as an API #693 & setuptools is a requirement #593)
• Utilizes the standard library, improving compatibility and reducing overhead.