Invoke TxGraph::DoWork() at appropriate times

src/txmempool.h

@@ -55,6 +55,10 @@ static const uint32_t MEMPOOL_HEIGHT = 0x7FFFFFFF;
  * iterations. */
 static constexpr uint64_t ACCEPTABLE_ITERS = 1'700;
 
+/** How much work we ask TxGraph to do after a mempool change occurs (either
+ * due to a changeset being applied, a new block being found, or a reorg). */
+static constexpr uint64_t POST_CHANGE_WORK = 5 * ACCEPTABLE_ITERS;
+
 /**
  * Test whether the LockPoints height and time are still valid on the current chain
  */