1) Fix mempool limiting for PrioritiseTransaction
Redo the feerate index to be based on mining score, rather than fee.
Update mempool_packages.py to test prioritisetransaction's effect on
package scores.
2) Update replace-by-fee logic to use fee deltas
3) Use fee deltas for determining mempool acceptance
4) Remove GetMinRelayFee
One test in AcceptToMemoryPool was to compare a transaction's fee
agains the value returned by GetMinRelayFee. This value was zero for
all small transactions. For larger transactions (between
DEFAULT_BLOCK_PRIORITY_SIZE and MAX_STANDARD_TX_SIZE), this function
was preventing low fee transactions from ever being accepted.
With this function removed, we will now allow transactions in that range
with fees (including modifications via PrioritiseTransaction) below
the minRelayTxFee, provided that they have sufficient priority.
Github-Pull: #7062
Rebased-From: eb306664e79ef2a2560327fae3484c901b01d674
Reduce the default limits on maximum number of transactions and the cumulative size of those transactions in both ancestor and descendant packages to 25 txs and 101kb total size.
Associate with each CTxMemPoolEntry all the size/fees of descendant
mempool transactions. Sort mempool by max(feerate of entry, feerate
of descendants). Update statistics on-the-fly as transactions enter
or leave the mempool.
Also add ancestor and descendant limiting, so that transactions can
be rejected if the number or size of unconfirmed ancestors exceeds
a target, or if adding a transaction would cause some other mempool
entry to have too many (or too large) a set of unconfirmed in-
mempool descendants.
