autopilot: update AttachmentHeuristics with context

Continue threading context through the autopilot system and remove the
remaining context.TODOs.

autopilot/agent_test.go

@@ -86,9 +86,9 @@ func (m *mockHeuristic) Name() string {
 	return "mock"
 }
 
-func (m *mockHeuristic) NodeScores(g ChannelGraph, chans []LocalChannel,
-	chanSize btcutil.Amount, nodes map[NodeID]struct{}) (
-	map[NodeID]*NodeScore, error) {
+func (m *mockHeuristic) NodeScores(_ context.Context, g ChannelGraph,
+	chans []LocalChannel, chanSize btcutil.Amount,
+	nodes map[NodeID]struct{}) (map[NodeID]*NodeScore, error) {
 
 	if m.nodeScoresArgs != nil {
 		directive := directiveArg{