Edit history from formerRepresentations

Pleroma and Akkoma send a post's earlier versions with it. A post PrivaPub first meets after its edits now has its
history, and an edit that carries them brings the versions missed in between; each is read as the post itself is. The
Akkoma scenario checks a post fetched after two edits by an account no persona follows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

FEDERATION.md

@@ -248,6 +248,8 @@ tags.
 content, one per choice, counted once per voter. Counts are refreshed with an `Update{Question}` at most every three
 minutes. Our own votes on other servers' polls are sent the same way to the poll's author only, without `published`.
 An incoming `Update` without a newer `updated` only refreshes counts and details; it is never recorded as an edit.
+A post's earlier versions in `formerRepresentations` (Pleroma, Akkoma) are its edit history, read as the post itself is:
+a post first met after its edits has them, and an edit that carries them brings the versions missed in between.
 
 **Quotes** (FEP-044f, with the older keys):
 - **Received.** A quote is read from `quote`, `quoteUrl`, `quoteUri`, `_misskey_quote` or a FEP-e232 `Link` tag.