Add WalletDb Initialization to MempoolNode::new() in src/mempool.rs

[Sophie-Ag00001]

PR Title: Add WalletDb Initialization to MempoolNode::new()

Summary of Changes

This pull request introduces WalletDb initialization within the MempoolNode::new() function located in src/mempool.rs. The implementation parallels the WalletDb setup found in the Miner module, aiming to integrate wallet functionalities directly into the mempool node context.

Motivation

The enhancement is intended to provide wallet-related capabilities in the mempool context, facilitating smoother interactions and potential integrations with wallet features without modifying other components beyond the specified file.

Relevant Context

The initial request specified a need to replicate the WalletDb initialization from src/miner.rs, ensuring consistency across modules and extending wallet functionalities in the mempool handling process. This change is crucial for users who require access to wallet features while working with the mempool.

Instructions for Testing

1. Clone the repository and checkout to this branch.
2. Build the project to ensure the WalletDb integration has no compilation errors.
3. Run existing test cases to verify that the mempool functionality remains intact.
4. If applicable, create unit tests for the MempoolNode::new() function to validate WalletDb initialization.

Known Issues

Currently, there are no known issues or limitations associated with this implementation. Further testing may uncover edge cases that warrant attention.

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We appreciate your review of this update and welcome any feedback!