Introduce RespondOnLimit() vs. OnLimit() methods

[VojtechVitek]

Split the new .OnLimit() method into two explicit methods.

1. RespondOnLimit() sends HTTP response
2. OnLimit() doesn't

The OnLimit() method will be useful to use with tools like https://github.com/webrpc/webrpc, which always return some JSON payload and can't halt further request execution like regular HTTP handlers.

[github-actions]

Benchmark Results

goos: linux
goarch: amd64
pkg: github.com/go-chi/httprate
cpu: AMD EPYC 7763 64-Core Processor                
               │ master.txt  │               pr.txt               │
               │   sec/op    │   sec/op     vs base               │
LocalCounter-4   19.56m ± 1%   19.89m ± 1%  +1.69% (p=0.003 n=10)

               │  master.txt  │             pr.txt             │
               │     B/op     │     B/op      vs base          │
LocalCounter-4   2.832Mi ± 0%   2.833Mi ± 0%  ~ (p=0.481 n=10)

               │ master.txt  │            pr.txt             │
               │  allocs/op  │  allocs/op   vs base          │
LocalCounter-4   121.4k ± 0%   121.5k ± 0%  ~ (p=0.493 n=10)