refactor(spv): isolate btcd script classification

[mswilkison]

Summary

• replace pkg/maintainer/spv's direct txscript classification with the existing bitcoin.GetScriptType abstraction
• preserve P2PKH, P2WPKH, P2SH, and P2WSH handling
• remove the last direct btcd import from pkg/maintainer/spv

Testing

• go test ./pkg/bitcoin
• go test ./pkg/maintainer/spv
• go test -count=1 ./pkg/maintainer/...

Fixes #3677

Summary by CodeRabbit

• Refactor
  • Updated transaction input classification to use the application’s Bitcoin script type handling.
  • Preserved existing detection and validation behavior for main and deposit inputs.
  • Removed an unnecessary underlying script-processing dependency.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: a2d8091b-2af9-42d5-9b18-edf390bf8127

📥 Commits

Reviewing files that changed from the base of the PR and between 038b7ce and 74ffd53.

📒 Files selected for processing (1)

• pkg/maintainer/spv/deposit_sweep.go

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📝 Walkthrough

Walkthrough

The deposit sweep parser now classifies transaction inputs through bitcoin.GetScriptType and bitcoin script constants, removing its direct btcd/txscript dependency while preserving existing main-UTXO and deposit-input handling.

Changes

SPV script classification

Layer / File(s)	Summary
Use bitcoin script types pkg/maintainer/spv/deposit_sweep.go	Replaces txscript checks with bitcoin script-type checks for P2PKH/P2WPKH main UTXOs and P2SH/P2WSH deposit inputs, and removes the unused import.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: moving SPV script classification away from direct btcd usage.
Linked Issues check	✅ Passed	The change removes direct btcd usage from pkg/maintainer/spv and routes script classification through pkg/bitcoin as required.
Out of Scope Changes check	✅ Passed	The PR is narrowly scoped to the btcd dependency refactor in pkg/maintainer/spv with no evident unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/spv-remove-btcd-dependency

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[mswilkison]

CI note: I reran the non-required client-integration-test after its initial failure. The rerun failed for the same shared external-infrastructure reason as PR #4167: all 30 failures are fulcrum_tcp cases receiving dial tcp 193.30.123.70:50001: connect: connection refused; every other package passed. This endpoint is not touched by this patch, and the matching result on an unrelated PR confirms this is not a regression here. Rerun job: https://github.com/threshold-network/keep-core/actions/runs/29531102639/job/87752372643