Require the Python version used by the client

[jsachs]

Summary

Require Python 3.10 or newer in the package metadata.

Problem

The project declares support for Python 3.8 and newer:

requires-python = ">=3.8"

However, the client uses Python 3.10 syntax, including structural pattern matching:

match config.grant_type:

and PEP 604 union annotations:

str | None

Users on Python 3.8 or 3.9 can install the package successfully, but importing it fails with a syntax error.

Fix

Update the package metadata to require Python 3.10 or newer:

requires-python = ">=3.10"

This prevents installation into unsupported Python environments and accurately reflects the language features used by the client.