rmcp-v2.1.0

Added

• add SEP-414 trace context meta accessors (#910)
• add SEP-2575 meta helpers (#942)

Fixed

• (transport) make AsyncRwTransport::receive cancel-safe (#941) (#947)
• (auth) preserve refresh_token when refresh response omits it (#949)
• block redirect header leaks (#936)
• don't respond to unparsable messages (#940)
• negotiate protocol version in handler (#930)