Join retry logic ignores receiver_version and fails for VersionUnknown

[zxch3n]

rust/loro-websocket-client/src/lib.rs:574-620, rust/loro-websocket-client/src/lib.rs:792-807

• The plain join_loro path returns an error immediately if the server responds with
  JoinError::VersionUnknown, so clients never rewind.
• The adaptor-based join loop does retry, but it discards the receiver_version field, never handing it to
  the adaptor or using it as the next attempt’s version.
• Result: reconnects to a server that prunes history fail unless the server still has every update since the
  client’s last counter.
• Fix: plumb receiver_version into retry logic (and surface it to get_alternative_version). Mirror that
  retry in the non-adaptor join_loro path so plain Loro docs also resync correctly.