Let `TxBuilder` avoid previously used UTXOs (UTXO locking)

[tnull]

Describe the enhancement
When sequentially creating multiple transactions, TxBuilder might currently reuse the same UTXOs, potentially exposing us to double-spend ourselves if we want to bring all of these generated transactions on-chain. It would be nice if the TxBuilder could track the used UTXOs internally, and allow to auto-unlock them after a set amount of time.

Use case
This is important for sequentially opening multiple Lightning channels, e.g., in LDK Node.