fix: prefer finalize_signed_extrinsic in engine

[dandanlen]

See #3557 - this should have been cherry-picked to main but wasn't.

[codecov]

Codecov Report

Merging #3956 (7d3c74b) into main (a841d84) will increase coverage by 0%.
Report is 1 commits behind head on main.
The diff coverage is 40%.

@@          Coverage Diff          @@
##            main   #3956   +/-   ##
=====================================
  Coverage     72%     72%           
=====================================
  Files        366     366           
  Lines      56789   56790    +1     
  Branches   56789   56790    +1     
=====================================
+ Hits       40947   40953    +6     
+ Misses     13756   13751    -5     
  Partials    2086    2086           

Files Changed	Coverage Δ
engine/src/p2p/peer_info_submitter.rs	0% <0%> (ø)
engine/src/witness/btc.rs	61% <0%> (ø)
...ked_chain_source/chunked_by_time/chain_tracking.rs	0% <0%> (ø)
engine/src/witness/dot.rs	47% <0%> (ø)
engine/src/witness/eth/erc20_deposits.rs	0% <0%> (ø)
engine/src/witness/eth/ethereum_deposits.rs	34% <0%> (ø)
engine/src/witness/eth/key_manager.rs	0% <0%> (ø)
engine/src/witness/eth/state_chain_gateway.rs	0% <0%> (ø)
engine/src/witness/eth/vault.rs	0% <0%> (ø)
engine/src/state_chain_observer/sc_observer/mod.rs	37% <59%> (ø)
... and 1 more

... and 7 files with indirect coverage changes

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