2.0.0

• BACKWARDS INCOMPATIBLE The concrete client implementations were refactored:
  • AsyncSMTPClient and SyncSMTPClient were refactored into "session factories", and thus are no longer used as context managers
  • The send_message() method is now reentrant, as it now creates (and closes) an ad-hoc session with the SMTP server
  • The connect() method now returns a context manager that yields an SMTP session
• BACKWARDS INCOMPATIBLE The OAuth2Authenticator class was refactored:
  • The return type of get_token() was changed to a (decoded) JSON web token – a dict containing the access_token and expires_in fields
  • The result of get_token() method is now automatically cached until the token's expiration time nears (configurable via the grace_period parameter in OAuth2Authenticator)
  • Added the clear_cached_token() method
• Dropped support for Python 3.7
• Upgraded minimum AnyIO version to 4.2+
• The Bcc and Resent-Bcc are now properly added to the recipients list by the concrete client implementation
• The Bcc and Resent-Bcc headers are now automatically left out of the data in SMTPClientProtocol.data() to simplify client implementations