walletkit: expose virtual PSBT transport requests

[darioAnongba]

Summary

• Add SDK request/response types for full virtual PSBT commit and publish/log flows.
• Wire gRPC and REST wrappers for anchor funding, change output selection, lock metadata, skip funding, skip broadcast, and publish labels.
• Update TxBuilder to call the full WalletKit request-object methods with its default anchor funding parameters.

Validation

• make fmt
• go vet ./...
• make lint workers=4
• make unit

Refs #145
Refs #157