- Add extract_auth_type() fallback for Windows Interactive where
  process_connection_string returns auth_type=None (DDBC handles
  auth natively but bulkcopy needs it for Azure Identity)
- Preserve auth_type in fallthrough return so bulkcopy can attempt
  fresh token acquisition even when connect-time token fails
- Fix get_raw_token docstring to match actual credential behavior
- Use 'is None' instead of '== None' in test assertion

Raises ValueError with supported types instead of KeyError when an
unsupported auth_type is passed to _acquire_token.

…llthrough return, clean up extract_auth_type parsing