feat: add height and hash to the Stump

[luisschwab]

This PR adds the height and hash to the Stump, so we can just de/serialize it to transfer validation across devices.

Maybe closes #80

[luisschwab]

Thoughts on this one @Davidson-Souza? This would require always passing height+hash when updating the accumulator. I don't think this would be a hassle on Floresta, but may be for other users.

[Davidson-Souza]

Hmm, not sure. Rustreexo is meant to be "bitcoin agnostic", only accumulator stuff. In theory you can use it with any database, not only the UTXO set. This would break this fundamental design principle

[luisschwab]

Perhaps adding a wrapper type on floresta with the Stump and these extra fields?

[Davidson-Souza]

Perhaps adding a wrapper type on floresta with the Stump and these extra fields?

We will change accumulator implementation soon for caching. But I think we can have something like this used for export/import only inside floresta.