The token bucket

Implement TokenBucket(rate, capacity) with allow(now): - refills rate tokens per second of elapsed time, capped at capacity (first call initializes the clock without refilling) - a request succeeds iff at least 1 full token is available; it consumes exactly 1 - now is a float timestamp — never call time functions yourself (the bucket must be deterministic) Burst of capacity at t=0 passes instantly; sustained throughput never exceeds rate per second.

Difficulty: advanced