clusterlin: use 'cost' terminology instead of 'iters' (refactor)

src/txgraph.h

@@ -102,10 +102,10 @@ public:
     virtual void SetTransactionFee(const Ref& arg, int64_t fee) noexcept = 0;
 
     /** TxGraph is internally lazy, and will not compute many things until they are needed.
-     *  Calling DoWork will perform some work now (controlled by iters) so that future operations
+     *  Calling DoWork will perform some work now (controlled by max_cost) so that future operations
      *  are fast, if there is any. Returns whether all currently-available work is done. This can
      *  be invoked while oversized, but oversized graphs will be skipped by this call. */
-    virtual bool DoWork(uint64_t iters) noexcept = 0;
+    virtual bool DoWork(uint64_t max_cost) noexcept = 0;
 
     /** Create a staging graph (which cannot exist already). This acts as if a full copy of
      *  the transaction graph is made, upon which further modifications are made. This copy can
@@ -257,7 +257,7 @@ public:
  *  and on the sum of transaction sizes within a cluster.
  *
  * - max_cluster_count cannot exceed MAX_CLUSTER_COUNT_LIMIT.
- * - acceptable_iters controls how many linearization optimization steps will be performed per
+ * - acceptable_cost controls how much linearization optimization work will be performed per
  *   cluster before they are considered to be of acceptable quality.
  * - fallback_order determines how to break tie-breaks between transactions:
  *   fallback_order(a, b) < 0 means a is "better" than b, and will (in case of ties) be placed
@@ -266,7 +266,7 @@ public:
 std::unique_ptr<TxGraph> MakeTxGraph(
     unsigned max_cluster_count,
     uint64_t max_cluster_size,
-    uint64_t acceptable_iters,
+    uint64_t acceptable_cost,
     const std::function<std::strong_ordering(const TxGraph::Ref&, const TxGraph::Ref&)>& fallback_order
 ) noexcept;