Dust Expiry: Clean the UTXO set from spam

When designing systems that deal with transactions, it is crucial to ensure the security and integrity of the data being handled. A particular point of concern arises when considering the structure and content of transaction inputs. One common practice is to reference transaction inputs using the "txid:vout" format. This method is favored because it directly corresponds to what is required to formulate a valid transaction input. However, there's a temptation to modify or omit certain elements of this data, such as the "scriptPubKey".

The "scriptPubKey" can be seen as an additional piece of information that, while not strictly necessary for identifying a transaction input, plays a critical role in the verification and execution of transactions. Some might consider removing this element or replacing it with a hash value to streamline the data or for other reasons. The underlying idea might be to request this piece of data from users as needed, rather than storing it directly. Yet, this approach introduces significant risks.

Removing or altering the representation of "scriptPubKey" within the system could lead to a degradation of cryptographic security. Such changes could inadvertently weaken the node's ability to validate transactions accurately. In the worst-case scenario, this might even lead to the acceptance of invalid transactions. The integrity of transaction processing and validation mechanisms is paramount in any system that handles digital currencies or similar assets. Therefore, maintaining a robust cryptographic foundation by preserving essential elements like the "txid:vout" and "scriptPubKey" in their conventional form is not just a matter of best practice but a fundamental requirement for ensuring the security and reliability of the node.