Naming, layout and comments: descriptive full-word names, one item per line in wrapped calls and literals, and doc comments on exported names

Short and single-letter names in application code become full words (tests
keep theirs). Wrapped calls, signatures and composite literals put one item
per line, and one-line function bodies are expanded. Exported names and
groups of constants get doc comments, and comments refer to the renamed
identifiers.

internal/mock/findatender/catalog_test.go

@@ -33,8 +33,13 @@ func TestEmbeddedCatalogIsValid(t *testing.T) {
 	}
 	if len(cat.Buyers) == 0 || len(cat.Suppliers) == 0 || len(cat.Subjects) == 0 ||
 		len(cat.Methods) == 0 {
-		t.Fatalf("embedded catalog has an empty pool: %d buyers, %d suppliers, %d subjects, %d methods",
-			len(cat.Buyers), len(cat.Suppliers), len(cat.Subjects), len(cat.Methods))
+		t.Fatalf(
+			"embedded catalog has an empty pool: %d buyers, %d suppliers, %d subjects, %d methods",
+			len(cat.Buyers),
+			len(cat.Suppliers),
+			len(cat.Subjects),
+			len(cat.Methods),
+		)
 	}
 }
 
@@ -42,8 +47,13 @@ func TestParseCatalog(t *testing.T) {
 	cat := loadTestCatalog(t)
 	if len(cat.Buyers) != 2 || len(cat.Suppliers) != 1 || len(cat.Subjects) != 2 ||
 		len(cat.Methods) != 2 {
-		t.Fatalf("got %d buyers, %d suppliers, %d subjects, %d methods",
-			len(cat.Buyers), len(cat.Suppliers), len(cat.Subjects), len(cat.Methods))
+		t.Fatalf(
+			"got %d buyers, %d suppliers, %d subjects, %d methods",
+			len(cat.Buyers),
+			len(cat.Suppliers),
+			len(cat.Subjects),
+			len(cat.Methods),
+		)
 	}
 	if d := cat.Buyers[0].Details; d == nil || len(d.Classifications) != 1 ||
 		d.Classifications[0].Scheme != "UK_CA_TYPE" {