feat: fetch note asset and fee asset witnesses before transaction execution

[PhilippGackstatter]

Removes the temporary code for lazy loading note asset witnesses during the prologue and instead pre-fetches them from the DataStore.

This means changing the DataStore::get_transaction_inputs to take a set of AssetVaultKeys and returning a set of AssetWitnesses. The data store is expected to also return an asset witness for the fee asset, since it will also be needed unconditionally, and it does not have to be loaded in TransactionExecutorHost::on_before_tx_fee_removed_from_account anymore.

The asset witnesses are stored in TransactionInputs, though other options exist, like returning (TransactionInputs, Vec<AssetWitness>) from TransactionExecutor::prepare_tx_inputs. This option is a bit nicer, but adds more duplicate data in TransactionInputs, since the asset witnesses will be contained in AdviceInputs at the end of the transaction.

TransactionContext::execute_code did not call into the DataStore so far, and so the asset witnesses were never fetched, causing test failures. This was changed to also call DataStore::get_transaction_inputs to load the witnesses. I'm hoping this could be done more nicely when splitting the TransactionContextBuilder into two APIs as mentioned under Internal API Changes in #1919.

closes #1852

[bobbinth]

Looks good! Thank you! I left just a couple of small comments/questions inline.

[igamigo]

Left a couple comments/questions on the implementation (one involving a potential different design), but looks good to me!

[bobbinth]

All looks good! Thank you!