This PR is a follow up to #18038 which introduced the idea of an unbroadcast set & focuses mostly on documentation updates and test fixes. One small functionality update to not throw an expected error in LoadMempool
when you upgrade software versions.
#18895 is another follow up to that addresses other functionality updates.
Background context:
The unbroadcast set is a mechanism for the mempool to track locally submitted transactions (via wallet or RPC). The node does a best-effort of delivering the transactions to the network via retries every 10-15 minutes until either a GETDATA
is received or the transaction is removed from the mempool.