feat(cooler): Cache.Pull returns and removes a value atomically

- Cache.Pull(ctx, key) ([]byte, bool, error), Laravel's Cache::pull
- Redis driver runs GETDEL (Redis 6.2+); memory driver uses otter Compute
  with InvalidateOp under the per-key lock; expired keys report not found
- TestPullSmoke over the memory driver and miniredis, ExampleCache_Pull
- README and docs/services/caching.md ("One-time values")

modules/cooler/example_test.go

@@ -48,6 +48,36 @@ func ExampleFromApp() {
 	// Output: [Hello Summer] 1
 }
 
+func ExampleCache_Pull() {
+	// A one-time code: one request stores it with a short TTL, the request
+	// that redeems it pulls it, and a second redemption finds nothing.
+	cache, err := cooler.NewMemoryCache("acme:", cooler.DefaultMaxEntries)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	ctx := context.Background()
+	if err := cache.Set(ctx, "signin:4f9c", []byte(`{"user_id":7}`), 5*time.Minute); err != nil {
+		fmt.Println(err)
+		return
+	}
+	for range 2 {
+		payload, ok, err := cache.Pull(ctx, "signin:4f9c")
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+		if !ok {
+			fmt.Println("unknown, expired or already used")
+			continue
+		}
+		fmt.Println(string(payload))
+	}
+	// Output:
+	// {"user_id":7}
+	// unknown, expired or already used
+}
+
 // Article is a blog's article model.
 type Article struct {
 	Slug string