PKCE Code Verifier and Challenge Generator

The `pkce` library is a lightweight Python module designed to simplify the generation of Proof Key for Code Exchange (PKCE) code verifiers and code challenges. It provides essential cryptographic helper functions for implementing the PKCE extension to the OAuth 2.0 Authorization Code Flow, particularly important for public clients (like mobile or single-page applications) that cannot securely store a client secret. The current version is 1.0.3, with an infrequent release cadence reflecting its stable and focused functionality.