refactor(key-wallet): update transaction builder to centralize funding and signing logic

[ZocoLini]

Centralizes coin selection, change derivation, BIP-69 sorting, fee accounting and input signing inside TransactionBuilder so per-tx-type helpers (build_and_sign_transaction, build_asset_lock, build_asset_lock_with_signer, …) only set up the builder and post-process wallet state.

Highlights

• TransactionBuilder owns the build pipeline: set_funding / set_change_address / set_current_height / set_selection_strategy / set_special_payload → build_unsigned() or build_signed(signer, path_resolver).
• New TransactionSigner trait with default sign_tx flow; blanket impl for Wallet (soft-wallet path) and for S: Signer (external signers). The blind-digest support check lives once, in the blanket impl.
• AssetLock-specific structural rules (OP_RETURN burn at tx.output[0], version-3 wire, BIP-69 skip, total-output derived from payload credit_outputs) are handled inside assemble_unsigned; helpers no longer mirror credit_outputs as raw outputs.
• dashcore payload structs (AssetLockPayload, CoinbasePayload, ProviderRegistrationPayload, …) gain CURRENT_VERSION constants and new(...) constructors so callers don't repeat version literals.

Note: The unit-test suite was not rewritten. Tests were only adjusted to match the new API

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📥 Commits

Reviewing files that changed from the base of the PR and between 49c8c6d and b462fc0.

📒 Files selected for processing (11)

• dash/src/blockdata/transaction/special_transaction/asset_lock.rs
• dash/src/blockdata/transaction/special_transaction/coinbase.rs
• dash/src/blockdata/transaction/special_transaction/provider_registration.rs
• dash/src/blockdata/transaction/special_transaction/provider_update_registrar.rs
• dash/src/blockdata/transaction/special_transaction/provider_update_revocation.rs
• dash/src/blockdata/transaction/special_transaction/provider_update_service.rs
• key-wallet-ffi/src/transaction.rs
• key-wallet-manager/src/lib.rs
• key-wallet/src/wallet/managed_wallet_info/asset_lock_builder.rs
• key-wallet/src/wallet/managed_wallet_info/transaction_builder.rs
• key-wallet/src/wallet/managed_wallet_info/transaction_building.rs

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/transaction-builder-signing

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[github-actions]

This PR has merge conflicts with the base branch. Please rebase or merge the base branch into your branch to resolve them.

[codecov]

Codecov Report

❌ Patch coverage is 58.88078% with 169 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.74%. Comparing base (49c8c6d) to head (b462fc0).

Files with missing lines	Patch %	Lines
...ction/special_transaction/provider_registration.rs	0.00%	34 Missing ⚠️
...ion/special_transaction/provider_update_service.rs	0.00%	26 Missing ⚠️
.../wallet/managed_wallet_info/transaction_builder.rs	87.77%	22 Missing ⚠️
...n/special_transaction/provider_update_registrar.rs	0.00%	20 Missing ⚠️
...ckdata/transaction/special_transaction/coinbase.rs	0.00%	18 Missing ⚠️
...wallet/managed_wallet_info/transaction_building.rs	71.92%	16 Missing ⚠️
.../special_transaction/provider_update_revocation.rs	0.00%	14 Missing ⚠️
key-wallet-ffi/src/transaction.rs	0.00%	9 Missing ⚠️
...data/transaction/special_transaction/asset_lock.rs	0.00%	6 Missing ⚠️
key-wallet-manager/src/lib.rs	0.00%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@              Coverage Diff              @@
##           v0.42-dev     #744      +/-   ##
=============================================
+ Coverage      71.31%   71.74%   +0.43%     
=============================================
  Files            321      321              
  Lines          70339    70013     -326     
=============================================
+ Hits           50160    50234      +74     
+ Misses         20179    19779     -400     

Flag	Coverage Δ
core	76.30% <0.00%> (-0.39%)	⬇️
ffi	47.38% <0.00%> (+2.40%)	⬆️
rpc	20.00% <ø> (ø)
spv	87.42% <ø> (-0.09%)	⬇️
wallet	70.75% <85.21%> (+0.90%)	⬆️

Files with missing lines	Coverage Δ
key-wallet-manager/src/lib.rs	75.00% <0.00%> (-0.26%)	⬇️
...c/wallet/managed_wallet_info/asset_lock_builder.rs	82.77% <95.55%> (+3.15%)	⬆️
...data/transaction/special_transaction/asset_lock.rs	65.11% <0.00%> (-10.56%)	⬇️
key-wallet-ffi/src/transaction.rs	0.00% <0.00%> (ø)
.../special_transaction/provider_update_revocation.rs	46.87% <0.00%> (-13.13%)	⬇️
...wallet/managed_wallet_info/transaction_building.rs	88.59% <71.92%> (+6.25%)	⬆️
...ckdata/transaction/special_transaction/coinbase.rs	85.11% <0.00%> (-10.22%)	⬇️
...n/special_transaction/provider_update_registrar.rs	86.27% <0.00%> (-12.98%)	⬇️
.../wallet/managed_wallet_info/transaction_builder.rs	84.90% <87.77%> (+23.82%)	⬆️
...ion/special_transaction/provider_update_service.rs	81.81% <0.00%> (-6.12%)	⬇️
... and 1 more

... and 21 files with indirect coverage changes