Constant RATE_LIMITER 

pub const RATE_LIMITER: &str = "machine RateLimiter<K> {\r\n    state Available(tokens: i64, max_tokens: i64)\r\n    state Exhausted(retry_after_ms: i64, max_tokens: i64)\r\n\r\n    transition acquire: Available -> Available | Exhausted\r\n    transition refill: Exhausted -> Available\r\n\r\n    effect now_ms() -> i64\r\n\r\n    on acquire() {\r\n        if tokens > 0 {\r\n            goto Available(tokens - 1, max_tokens);\r\n        } else {\r\n            goto Exhausted(perform now_ms(), max_tokens);\r\n        }\r\n    }\r\n\r\n    on refill() {\r\n        goto Available(max_tokens, max_tokens);\r\n    }\r\n}\r\n";

The Gust source for the RateLimiter machine.

A token-bucket rate limiter with two states:

• Available – tokens remain; requests can proceed.
• Exhausted – no tokens left; a retry_after_ms value indicates when tokens will be replenished.

Generic over K for the rate-limit key type.