core, eth, les, tests, trie: abstract node scheme (#25532)

This PR introduces a node scheme abstraction. The interface is only implemented by `hashScheme` at the moment, but will be extended by `pathScheme` very soon.

Apart from that, a few changes are also included which is worth mentioning:

-  port the changes in the stacktrie, tracking the path prefix of nodes during commit
-  use ethdb.Database for constructing trie.Database. This is not necessary right now, but it is required for path-based used to open reverse diff freezer

core/state/iterator_test.go

@@ -26,10 +26,10 @@ import (
 // Tests that the node iterator indeed walks over the entire database contents.
 func TestNodeIteratorCoverage(t *testing.T) {
 	// Create some arbitrary test state to iterate
-	db, root, _ := makeTestState()
-	db.TrieDB().Commit(root, false, nil)
+	db, sdb, root, _ := makeTestState()
+	sdb.TrieDB().Commit(root, false, nil)
 
-	state, err := New(root, db, nil)
+	state, err := New(root, sdb, nil)
 	if err != nil {
 		t.Fatalf("failed to create state trie at %x: %v", root, err)
 	}
@@ -42,19 +42,19 @@ func TestNodeIteratorCoverage(t *testing.T) {
 	}
 	// Cross check the iterated hashes and the database/nodepool content
 	for hash := range hashes {
-		if _, err = db.TrieDB().Node(hash); err != nil {
-			_, err = db.ContractCode(common.Hash{}, hash)
+		if _, err = sdb.TrieDB().Node(hash); err != nil {
+			_, err = sdb.ContractCode(common.Hash{}, hash)
 		}
 		if err != nil {
 			t.Errorf("failed to retrieve reported node %x", hash)
 		}
 	}
-	for _, hash := range db.TrieDB().Nodes() {
+	for _, hash := range sdb.TrieDB().Nodes() {
 		if _, ok := hashes[hash]; !ok {
 			t.Errorf("state entry not reported %x", hash)
 		}
 	}
-	it := db.DiskDB().NewIterator(nil, nil)
+	it := db.NewIterator(nil, nil)
 	for it.Next() {
 		key := it.Key()
 		if bytes.HasPrefix(key, []byte("secure-key-")) {