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/middleware/ratelimit_test.go

@@ -8,7 +8,8 @@ import (
 
 func TestRateLimit(t *testing.T) {
 	l := NewKeyedLimiter(t.Context(), 1, 2, 0)
-	h := RateLimit(l, nil)(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
+	h := RateLimit(l, nil)(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {
+	}))
 	var last int
 	for i := 0; i < 4; i++ {
 		rec := httptest.NewRecorder()