multi: context.Background() -> t.Context()

Use the new feature of Go 1.24, fix linter warnings.

This change was produced by:
 - running golangci-lint run --fix
 - sed 's/context.Background/t.Context/' -i `git grep -l context.Background | grep test.go`
 - manually fixing broken tests
 - itest, lntest: use ht.Context() where ht or hn is available
 - in HarnessNode.Stop() we keep using context.Background(), because it is
   called from a cleanup handler in which t.Context() is canceled already.

autopilot/prefattach_test.go

@@ -76,7 +76,7 @@ var chanGraphs = []struct {
 // empty graph, the NodeSores function always returns a score of 0.
 func TestPrefAttachmentSelectEmptyGraph(t *testing.T) {
 	t.Parallel()
-	ctx := context.Background()
+	ctx := t.Context()
 	prefAttach := NewPrefAttachment()
 
 	// Create a random public key, which we will query to get a score for.
@@ -116,7 +116,7 @@ func TestPrefAttachmentSelectEmptyGraph(t *testing.T) {
 // and the funds are appropriately allocated across each peer.
 func TestPrefAttachmentSelectTwoVertexes(t *testing.T) {
 	t.Parallel()
-	ctx := context.Background()
+	ctx := t.Context()
 
 	prand.Seed(time.Now().Unix())
 
@@ -203,7 +203,7 @@ func TestPrefAttachmentSelectTwoVertexes(t *testing.T) {
 // allocate all funds to each vertex (up to the max channel size).
 func TestPrefAttachmentSelectGreedyAllocation(t *testing.T) {
 	t.Parallel()
-	ctx := context.Background()
+	ctx := t.Context()
 
 	prand.Seed(time.Now().Unix())
 
@@ -316,7 +316,7 @@ func TestPrefAttachmentSelectGreedyAllocation(t *testing.T) {
 // of zero during scoring.
 func TestPrefAttachmentSelectSkipNodes(t *testing.T) {
 	t.Parallel()
-	ctx := context.Background()
+	ctx := t.Context()
 
 	prand.Seed(time.Now().Unix())