clusterlin: replace cluster linearization with SFL (feature)

This replaces the existing LIMO linearization algorithm (which internally uses
ancestor set finding and candidate set finding) with the much more performant
spanning-forest linearization algorithm.

This removes the old candidate-set search algorithm, and several of its tests,
benchmarks, and needed utility code.

The worst case time per cost is similar to the previous algorithm, so
ACCEPTABLE_ITERS is unchanged.

test/functional/mempool_packages.py

@@ -239,8 +239,9 @@ class MempoolPackagesTest(BitcoinTestFramework):
         self.generate(self.nodes[0], 1)
         self.trigger_reorg(fork_blocks, self.nodes[0])
 
-        # Check if the txs are returned to the mempool
-        assert_equal(self.nodes[0].getrawmempool(), mempool0)
+        # Check if the txs are returned to the mempool (though the transaction ordering may
+        # change as it is non-deterministic).
+        assert_equal(set(self.nodes[0].getrawmempool()), set(mempool0))
 
         # Clean-up the mempool
         self.generate(self.nodes[0], 1)