Silent payments tracking issue #55

Features

• Sending support and Broadcast transactions #51 silent payments: add sending support #64
• Persistence silent payments: file-backed wallet store #60
• File imports: JSON or binary format. Includes automatic file imports from configuration. silent payments: file-based key import/export #56
• Offline signer support (i.e. BitBox)
• Receiving silent payments: integrate SPDK scanning and wallet IPC #50

Kernel API

• Needs TxIn: Witness, ScriptSig kernel: expose witness stack and scriptSig for btck_TransactionInput bitcoin/bitcoin#35380
• Nice to have ScriptPubkey::is_p2tr feat(core): Add zero-copy as_bytes to ScriptPubkeyExt sedited/rust-bitcoinkernel#190