2026.6.0 send support

[Timshel]

With 2026.6.0 the client now start by requiring an access_token.

Some remarks:

• Added auth/send.rs since I though that auth.rs was already long enough.

• Added the silent property to the Error to be use ErrorKind::Json without logging the error.
  Probably could be injected in some place like the Error::empty but wanted to keep modifications to a minimum.

  While adding another set of optional values to ConnectData I wondered if it could be converted to an Enum with a value for each grant_type ? I think it would be cleaner, but maybe I'm missing something ?