- limiterGroup.Allow(): return false immediately on first denial instead of
continuing through all limiters (wasting tokens on subsequent limiters).
Sort limiters by Limit() so most restrictive fires first.
- rateLimiter.Close(): add missing httpLoader.Close() to prevent resource leak.
- Add doc comments for all exported symbols (package, constants, Options,
NewRateLimiter, NewLimiter, ErrRateLimit, generators).
- Add rate_test.go with 59 unit tests covering generators, limiter groups,
parsing (limit/line/patterns), reload, loader merge, Close behavior,
and priority ordering (exact IP > CIDR > $$ > $).
ginuerzh