Avoid the fuzzer situation where:
1. Orphanage has 2 transactions with the same txid, one with witness,
one without witness.
2. The transaction with witness is found to have
`TX_INPUTS_NOT_STANDARD` error. The txid is added to recent rejects
filter, and the tx with witness is deleted from orphanage.
3. A low feerate parent is found. Find1P1CPackage finds the transaction
with no witness in orphanage, and returns the package.
4. net_processing has just been handed a package in which the child is
already in recent rejects.
This is a slight behavior change: if a transaction is in both
reconsiderable rejects and AlreadyHaveTx in another way, we don't try to
return a 1p1c package. This is the correct thing to do, as we don't want
to reconsider transactions that have multiple things wrong with them.
For example, if a transaction is low feerate, and then later found to
have a bad signature, we shouldn't try it again in a package.
This will become necessary in later commits that query mempool. We also
introduce the TxDownloadOptions in this commit to make the later diff
easier to review.
This module is going to be responsible for managing everything related
to transaction download, including txrequest, orphan transactions and
package relay. It will be responsible for managing usage of the
TxOrphanage and instructing PeerManager:
- what tx or package-related messages to send to which peer
- whether a tx or package-related message is allowed or useful
- what transactions are available to try accepting to mempool
Future commits will consolidate the interface and re-delegate
interactions from PeerManager to TxDownloadManager.
