A recorder captures events from a [tracing::span] and records them
to a [mpsc::UnboundedSender]. In order to record events, the recorder’s
layer (Recorder::layer) must be installed into the relevant tracing
subscriber.
A value that can appear in an entry. This custom
representation serves two purposes: 1) internally, to
to manage string buffer reuse; and 2) as a serialization
format that may be used with bincode.