graph/db+sqldb: improve efficiency of node migration

There is no need to use the "collect-then-update" pattern for node
insertion during the SQL migration since if we do have any previously
persisted data for the node and happen to re-run the insertion for that
node, the data will be exactly the same. So we can make use of "On
conflict, no nothing" here too.

sqldb/sqlc/queries/graph.sql

@@ -105,7 +105,9 @@ INSERT INTO graph_node_features (
     node_id, feature_bit
 ) VALUES (
     $1, $2
-);
+) ON CONFLICT (node_id, feature_bit)
+    -- Do nothing if the feature already exists for the node.
+    DO NOTHING;
 
 -- name: GetNodeFeatures :many
 SELECT *
@@ -135,7 +137,7 @@ WHERE node_id = $1
    ───────────────────────────────────<E29480><E29480>─────────
 */
 
--- name: InsertNodeAddress :exec
+-- name: UpsertNodeAddress :exec
 INSERT INTO graph_node_addresses (
     node_id,
     type,
@@ -143,7 +145,8 @@ INSERT INTO graph_node_addresses (
     position
 ) VALUES (
     $1, $2, $3, $4
- );
+) ON CONFLICT (node_id, type, position)
+    DO UPDATE SET address = EXCLUDED.address;
 
 -- name: GetNodeAddresses :many
 SELECT type, address