depgraph: add memory usage control (feature)

Co-Authored-By: Lőrinc <pap.lorinc@gmail.com>

src/cluster_linearize.h

@@ -12,6 +12,7 @@
 #include <utility>
 #include <vector>
 
+#include <memusage.h>
 #include <random.h>
 #include <span.h>
 #include <util/feefrac.h>
@@ -332,6 +333,17 @@ public:
         }
         return true;
     }
+
+    /** Reduce memory usage if possible. No observable effect. */
+    void Compact() noexcept
+    {
+        entries.shrink_to_fit();
+    }
+
+    size_t DynamicMemoryUsage() const noexcept
+    {
+        return memusage::DynamicUsage(entries);
+    }
 };
 
 /** A set of transactions together with their aggregate feerate. */