autopilot: start threading contexts through

The `GraphSource` interface in the `autopilot` package is directly
implemented by the `graphdb.KVStore` and so we will eventually thread
contexts through to this interface. So in this commit, we start updating
the autopilot system to thread contexts through in preparation for
passing the context through to any calls made to the GraphSource.

Two context.TODOs are added here which will be addressed in follow up
commits.

autopilot/simple_graph.go

@@ -1,5 +1,7 @@
 package autopilot
 
+import "context"
+
 // diameterCutoff is used to discard nodes in the diameter calculation.
 // It is the multiplier for the eccentricity of the highest-degree node,
 // serving as a cutoff to discard all nodes with a smaller hop distance. This
@@ -20,7 +22,7 @@ type SimpleGraph struct {
 // NewSimpleGraph creates a simplified graph from the current channel graph.
 // Returns an error if the channel graph iteration fails due to underlying
 // failure.
-func NewSimpleGraph(g ChannelGraph) (*SimpleGraph, error) {
+func NewSimpleGraph(ctx context.Context, g ChannelGraph) (*SimpleGraph, error) {
 	nodes := make(map[NodeID]int)
 	adj := make(map[int][]int)
 	nextIndex := 0
@@ -42,17 +44,22 @@ func NewSimpleGraph(g ChannelGraph) (*SimpleGraph, error) {
 		return nodeIndex
 	}
 
-	// Iterate over each node and each channel and update the adj and the node
-	// index.
-	err := g.ForEachNode(func(node Node) error {
+	// Iterate over each node and each channel and update the adj and the
+	// node index.
+	err := g.ForEachNode(ctx, func(ctx context.Context, node Node) error {
 		u := getNodeIndex(node)
 
-		return node.ForEachChannel(func(edge ChannelEdge) error {
-			v := getNodeIndex(edge.Peer)
+		return node.ForEachChannel(
+			ctx, func(_ context.Context,
+				edge ChannelEdge) error {
 
-			adj[u] = append(adj[u], v)
-			return nil
-		})
+				v := getNodeIndex(edge.Peer)
+
+				adj[u] = append(adj[u], v)
+
+				return nil
+			},
+		)
 	})
 	if err != nil {
 		return nil, err