refactor: use btc rpc client for mempool tracker

[kylezs]

Diff looks worse than it is, a bit of boilerplate in the tests and what not that may be able to be reduced further. Core logic and interfaces are all the same, so nothing breaking for web guys. Was just type wrangling mostly.

Pull Request

Closes: PRO-909

Checklist

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

• I am confident that the code works - have tested it running against localnet.
• I have updated documentation where appropriate.

Summary

Unifies the two btc clients we use so we only use one method of calling a BTC node. We also now share the same types making things more consistent.

Think there's more to do here, but this is a start.

[codecov]

Codecov Report

Merging #4227 (b2ef8ff) into main (9f336aa) will decrease coverage by 0%.
Report is 4 commits behind head on main.
The diff coverage is 0%.

@@          Coverage Diff           @@
##            main   #4227    +/-   ##
======================================
- Coverage     72%     71%    -0%     
======================================
  Files        383     383            
  Lines      62350   62834   +484     
  Branches   62350   62834   +484     
======================================
+ Hits       44631   44844   +213     
- Misses     15379   15654   +275     
+ Partials    2340    2336     -4     

Files	Coverage Δ
engine/src/dot/retry_rpc.rs	7% <0%> (ø)
engine/src/btc/retry_rpc.rs	9% <0%> (ø)
engine/src/btc/rpc.rs	0% <0%> (ø)

... and 37 files with indirect coverage changes

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[linear]

PRO-909 BTC part of ingress-egress tracker to use same BTC RPC as witnesser

There's currently a separate BTC RPC that's written for the ingress-egress tracker. We should unify them and use the (base i.e. not the retrier one) RPC client we have for the witnesser (of course, we may need to add some more methods to it.