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/memory.go

@@ -84,6 +84,27 @@ func (m *memoryCache) Get(_ context.Context, key string) ([]byte, bool, error) {
 	return clone(e.val), true, nil
 }
 
+// Pull returns the value at key and removes it under otter's per-key lock, so
+// of two concurrent callers at most one sees found=true. An expired entry is
+// removed too and reported as not found.
+func (m *memoryCache) Pull(_ context.Context, key string) ([]byte, bool, error) {
+	var (
+		out   []byte
+		found bool
+	)
+	now := time.Now()
+	m.c.Compute(m.key(key), func(old memEntry, ok bool) (memEntry, otter.ComputeOp) {
+		if !ok {
+			return old, otter.CancelOp
+		}
+		if !old.expired(now) {
+			out, found = clone(old.val), true
+		}
+		return memEntry{}, otter.InvalidateOp
+	})
+	return out, found, nil
+}
+
 func (m *memoryCache) Set(_ context.Context, key string, value []byte, ttl time.Duration) error {
 	e := memEntry{val: clone(value)}
 	if ttl > 0 {