fix: replace egress witnessing with change witnesser.

[dandanlen]

Pull Request

Closes: PRO-1655

Checklist

Please conduct a thorough self-review before opening the PR.

• I am confident that the code works. (Gonna wait until bouncer)
• I have written sufficient tests. (Tests are coming in other PRs)
• I have written and tested required migrations. (TODO)
• I have updated documentation where appropriate.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 10 lines in your changes missing coverage. Please review.

Project coverage is 70%. Comparing base (f4dd3db) to head (8c84438).
Report is 29 commits behind head on main.

Files with missing lines	Patch %	Lines
...te-chain/runtime/src/chainflip/solana_elections.rs	36%	8 Missing and 1 partial ⚠️
engine/src/witness/sol.rs	0%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #5252    +/-   ##
======================================
- Coverage     70%     70%    -0%     
======================================
  Files        486     485     -1     
  Lines      87289   87105   -184     
  Branches   87289   87105   -184     
======================================
- Hits       61298   61070   -228     
- Misses     22695   22733    +38     
- Partials    3296    3302     +6     

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[kylezs]

Closing as discussed.