Block template fees are calculated by looping over new_tmpl->vTxFees
and return (early) once the fee_threshold is exceeded.
This left an edge case when the mempool is empty, which this commit
fixes and adds a test for. It does so by using std::accumulate instead
of manual loops.
Also update interface_ipc.py to account for the new behavior.
Co-authored-by: Raimo33 <claudio.raimondi@protonmail.com>
This change should fix issue https://github.com/bitcoin/bitcoin/issues/33417
reported by zaidmstrr. It's possible to reproduce the `mp/proxy.capnp:0:
failed: Duplicate ID @0xcc316e3f71a040fb` error by installing libmultiprocess
system-wide, or to one of the locations listed in the python test's `imports`
list before the local libmultiprocess subtree, and then running the test.
