bugfix: enforce bitcoin rpc only for miner

[fdefelici]

Description

This patch addresses an issue in the BitcoinRegtestController where instantiating a BitcoinRpcClient required Bitcoin RPC credentials unconditionally.

While RPC credentials are indeed mandatory for nodes configured as miners, they should not be required for other node types (e.g., follower nodes), becase they don't use a RPC client at all.

Previously (before the RPC rollout in #6387), it was possible to instantiate an RPC client without credentials (even though this behavior is not supported by bitcoind).
In this patch, instead of permitting instantiation without authentication, I’ve made the BitcoinRegtestController’s behavior explicit and dependent on the node type:

• Miner node: requires both the Bitcoin Indexer and a valid Bitcoin RPC client.
• Other node (Follower/Signer): requires the Bitcoin Indexer, but does not need a Bitcoin RPC client.

The idea is to make the code behavior clearer around this scenario.

Is this reasoning correct?

Context:
This issue was surfaced by @Jiloc, on develop branch, during live testing with a follower node using:

cargo run --bin stacks-node -- start --config ./sample/conf/testnet-follower-conf.toml

Which resulted in the following error:

Process abort due to thread panic: panicked at stacks-node\src\burnchains\bitcoin_regtest_controller.rs:375:14:
unable to instantiate the RPC client!: MissingCredentials

Applicable issues

• fixes #

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

[fdefelici]

Just an heads-up:

• I also added some unit tests to check for BitcoinRegetestController creation behaviour depending on the node type, and
• fixed the tests::neon_integrations::antientropy_integration_test that was failing due to it was trying to generate bitcoin blocks (for testing purpose) using a follower node configuration.

[codecov]

Codecov Report

❌ Patch coverage is 82.48175% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.21%. Comparing base (895537e) to head (be46dbb).
⚠️ Report is 15 commits behind head on develop.

Files with missing lines	Patch %	Lines
...-node/src/burnchains/bitcoin_regtest_controller.rs	84.96%	20 Missing ⚠️
stacks-node/src/tests/neon_integrations.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6534      +/-   ##
===========================================
- Coverage    79.51%   79.21%   -0.31%     
===========================================
  Files          566      566              
  Lines       345340   345421      +81     
===========================================
- Hits        274596   273610     -986     
- Misses       70744    71811    +1067     

Files with missing lines	Coverage Δ
...-node/src/burnchains/rpc/bitcoin_rpc_client/mod.rs	98.05% <ø> (ø)
stacks-node/src/tests/neon_integrations.rs	38.52% <0.00%> (-11.68%)	⬇️
...-node/src/burnchains/bitcoin_regtest_controller.rs	68.97% <84.96%> (-6.60%)	⬇️

... and 96 files with indirect coverage changes

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[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.