WIP: feat: bitcoin elections

[kylezs]

WIP: This will become the base branch/PR for the conversion of the bitcoin witnessing to the new elections pallet.

Pull Request

Closes: PRO-1772

Checklist

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

• I am confident that the code works.
• I have written sufficient tests.
• I have written and tested required migrations.
• I have updated documentation where appropriate.

Summary

[codecov]

Codecov Report

Attention: Patch coverage is 24.03178% with 765 lines in your changes missing coverage. Please review.

Project coverage is 71%. Comparing base (acd6dd9) to head (5971673).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ctoral_systems/block_height_tracking/primitives.rs	0%	160 Missing and 2 partials ⚠️
...ons/src/electoral_systems/block_height_tracking.rs	13%	134 Missing and 3 partials ⚠️
engine/src/witness/btc_e.rs	0%	99 Missing ⚠️
...e-chain/runtime/src/chainflip/bitcoin_elections.rs	13%	75 Missing ⚠️
...e/src/state_chain_observer/client/electoral_api.rs	0%	69 Missing ⚠️
...elections/src/electoral_systems/block_witnesser.rs	68%	28 Missing and 22 partials ⚠️
...ectoral_systems/block_height_tracking/consensus.rs	0%	41 Missing ⚠️
engine/src/elections.rs	0%	26 Missing ⚠️
engine/src/btc/retry_rpc.rs	23%	23 Missing ⚠️
state-chain/custom-rpc/src/lib.rs	0%	20 Missing ⚠️
... and 13 more

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5457     +/-   ##
=======================================
- Coverage     72%     71%     -1%     
=======================================
  Files        495     506     +11     
  Lines      88356   89202    +846     
  Branches   88356   89202    +846     
=======================================
- Hits       63340   63012    -328     
- Misses     22448   23494   +1046     
- Partials    2568    2696    +128     

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