refactor: BitcoinRegtestController RPC roll out (STEP 7)

[fdefelici]

Description

This is the last PR related to the RPC roll out in BitcoinRegtestController

In this PR, has been:

• migrated BitcoinRPCRequest::list_unspent (now named BitcoinRegtestController::retrieve_utxo_set)
• reviewed BitcoinRegtestController::get_all_utxo
• reviewed BitcoinRegtestController::get_utxo
• removed BitcoinRPCRequest entirely
• moved/removed tests now belonging to BitcoinRegtestController
• small cleaning/refactoring to improve code related to this change
• increased tests coverage

Applicable issues

• fixes refactor: roll out new RPC client in BitcoinRegtestController #6387

Additional info (benefits, drawbacks, caveats)

Checklist

• Test coverage for new or modified code paths
• Changelog is updated
• Required documentation changes (e.g., docs/rpc/openapi.yaml and rpc-endpoints.md for v2 endpoints, event-dispatcher.md for new events)
• New clarity functions have corresponding PR in clarity-benchmarking repo
• New integration test(s) added to bitcoin-tests.yml

[codecov]

Codecov Report

❌ Patch coverage is 91.59292% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.39%. Comparing base (e864154) to head (0288c84).
⚠️ Report is 117 commits behind head on develop.

Files with missing lines	Patch %	Lines
...-node/src/burnchains/bitcoin_regtest_controller.rs	91.36%	19 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6451      +/-   ##
===========================================
- Coverage    80.01%   79.39%   -0.62%     
===========================================
  Files          558      559       +1     
  Lines       343239   343679     +440     
===========================================
- Hits        274634   272878    -1756     
- Misses       68605    70801    +2196     

Files with missing lines	Coverage Δ
...ode/src/burnchains/rpc/bitcoin_rpc_client/tests.rs	99.86% <100.00%> (+<0.01%)	⬆️
stacks-node/src/tests/mod.rs	72.26% <ø> (-0.94%)	⬇️
stacks-node/src/tests/neon_integrations.rs	32.13% <ø> (-19.33%)	⬇️
stackslib/src/chainstate/stacks/mod.rs	76.27% <100.00%> (-0.19%)	⬇️
...-node/src/burnchains/bitcoin_regtest_controller.rs	74.57% <91.36%> (+0.15%)	⬆️

... and 128 files with indirect coverage changes

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[Jiloc]

LGTM!

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.