transport: a pushed change written out by its size, never its bytes

Review 4, F3: the console writes each message out with `{:#?}`, and `SyncBody` derived
`Debug`, so `Changes` (changes pushed as they are) printed every byte of every change.
Pushes are the small messages, and Automerge deflates no change under 256 bytes: a
short value's path and value went into the console in clear, which any user with any
capability reads (the page's `messages` events, and since 1266 a subscribed node's
`messages/own/{seq}` too), paths it may not read included.

`SyncBody` now writes itself out with sizes for the changes, as `SyncPayload` does
for an Automerge message; heads and a delta's spec stay as they were.

0 files changed, 0 insertions, 0 deletions