Fix sending SyncMessage to self

[gferon]

Fixes sending SyncMessage and to self.

• After looking at both Signal-Android and Signal-Desktop, we need to make sure any message sent to self is never send unidentified
• Make sure we add padding to all SyncMessage
• Remove some redundant session loading before creating encrypted messages

[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (afb5114) 3.66% compared to head (d53df2a) 3.65%.

❗ Current head d53df2a differs from pull request most recent head bc8f646. Consider uploading reports for the commit bc8f646 to get more accurate results

Files	Patch %	Lines
libsignal-service/src/proto.rs	0.00%	9 Missing ⚠️
libsignal-service/src/sender.rs	0.00%	6 Missing ⚠️
libsignal-service/src/websocket.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #263      +/-   ##
========================================
- Coverage   3.66%   3.65%   -0.02%     
========================================
  Files         38      38              
  Lines       2809    2818       +9     
========================================
  Hits         103     103              
- Misses      2706    2715       +9     

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[direc85]

Looks good to me, assuming some on-device testing has been made!

[rubdos]

@gferon Shouldn't we make those stronger types, such that it's impossible to transmit without padding?

[gferon]

Yes, that was a ninja trick for the time being.