Implement Database::clone_to_path

[vlopes11]

Some testing might require the fuel-core/Database to be copied into new paths so different cases might be tested in isolation one from the other.

This issue requires a new fn clone_to_path<P>(&self, path: P) -> io::Result<Database> where P: AsRef<Path> method that will copy all database contents and initialize a new instance in the provided path, mirroring the behavior of Database::open

This is required to further extend the covered cases for benchmark, where we prepare a database that will be used for every iteration of the benchmark tool.