Send SyncMessages to self unidentified when possible

[direc85]

This changes the approach of sending SyncMessages quite a lot, yet it shouldn't be too invasive. This has received a brief test run in a device and it improves the situation quite a lot, if not fixes the core issue as-is! (knocks on wood)

• Add self-sync-message results to group and dm message sender results, and so...
• Return a Vec<...> from send_message()
• Accept the self recipient unidentified access when sending DMs
• Never send any "oridinary messages" to self, but only SyncMessages

I'll continue running this on my device for a while to see if there are any ill behaviors after this, and polish and fix as needed before un-drafting this.

[direc85]

Note that this also changes the API a bit, so let's try to be in sync with this :)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (1cc7517) 17.21% compared to head (4e8b4c6) 17.19%. Report is 14 commits behind head on main.

:exclamation: Current head 4e8b4c6 differs from pull request most recent head 7eabf87. Consider uploading reports for the commit 7eabf87 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #286 +/- ## ========================================== - Coverage 17.21% 17.19% -0.03% ========================================== Files 38 38 Lines 3073 3077 +4 ========================================== Hits 529 529 - Misses 2544 2548 +4 ```

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[direc85]

Superseded by #287 (and Whisperfish#594)

It turns out that sending SyncMessages nor Messages to self recipient identified works, so I'm closing this.