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/cooler.go

@@ -74,6 +74,11 @@ type Attempter interface {
 type Cache interface {
 	// Get returns the value at key and whether it was found.
 	Get(ctx context.Context, key string) ([]byte, bool, error)
+	// Pull returns the value at key and removes it in one atomic step, as
+	// Laravel's Cache::pull. found is false when the key is missing or
+	// expired; of two concurrent callers at most one gets found=true. The
+	// Redis driver uses GETDEL (Redis 6.2 or newer).
+	Pull(ctx context.Context, key string) ([]byte, bool, error)
 	// Set stores value at key for ttl (0 or less: no expiry).
 	Set(ctx context.Context, key string, value []byte, ttl time.Duration) error
 	// Has reports whether key holds a live value.