We have the `_raw_t` interface and a `_rw_t` specialized one. Many use cases only need a single counter like for instance the circuit creation DoS defense would use that. Or legacy/trac#15516 introduce2 rate limiting. After a discussion with nickm, it would be wise if we can simply implement a generic counter token bucket: ``` token_bucket_ctr_t ``` ... with a single bucket in it and thus could generically be used by many subsystems.