Improving Light Node Synchronization Speed

[yanguoyu]

Currently, during light node synchronization, each transaction input requires a fetch_transaction operation. If a transaction contains a large number of inputs, this can significantly slow down synchronization.

The purpose of fetch_transaction is to retrieve input details when get_transaction is called. However, it now seems unnecessary because:

1. We already filter out inputs not belonging to the wallet, so only wallet-related inputs are stored in the database.
2. If an input belongs to the wallet, the transaction that created its output cell should have been synchronized earlier.
   Thus, fetch_transaction would only fetch transactions irrelevant to the wallet.

While this reasoning holds in theory, actual code review and testing are still needed to verify whether other issues exist.