Fix flaky compactor tests due to timestamp race condition

The createClosedIssue helper was setting ClosedAt to time.Now(), but the
eligibility check uses '<= datetime(now, -0 days)'. This created a race
condition where if nanoseconds elapsed between issue creation and the
query, the issue would fail eligibility checks.

Changed to now.Add(-1*time.Second) to ensure issues are always eligible
when compact_tier1_days is set to 0 for testing.

Fixes bd-18

Amp-Thread-ID: https://ampcode.com/threads/T-bc303dd9-f0e7-4d52-8908-e433d429ac4a
Co-authored-by: Amp <amp@ampcode.com>

internal/compact/compactor_test.go

@@ -35,6 +35,7 @@ func createClosedIssue(t *testing.T, store *sqlite.SQLiteStorage, id string) *ty
 
 	ctx := context.Background()
 	now := time.Now()
+	closedAt := now.Add(-1 * time.Second)
 	issue := &types.Issue{
 		ID:    id,
 		Title: "Test Issue",
@@ -83,7 +84,7 @@ Testing strategy:
 		IssueType:  types.TypeTask,
 		CreatedAt:  now.Add(-48 * time.Hour),
 		UpdatedAt:  now.Add(-24 * time.Hour),
-		ClosedAt:   &now,
+		ClosedAt:   &closedAt,
 	}
 
 	if err := store.CreateIssue(ctx, issue, "test"); err != nil {