Redis backend with race check bug

[oskarwojciski]

After the fix from #22 I found a bug:
With a small amount of Takes from the bucket, where Backend is a Redis with raceCheck=true then sometimes the expected version is higher than the actual one.

To replicate the issue I created a simple test:

func (s *LimitersTestSuite) TestTokenBucketRealClockRaceCheckRedisProblem() {
	ttl := time.Second
	limit := int64(2)
	refillEvery := time.Duration(int64(ttl) / limit)
	locker := l.NewLockNoop()
	backend := l.NewTokenBucketRedis(s.redisClient, uuid.New().String(), ttl, true)

	clk := l.NewSystemClock()
	ctx := context.Background()

	bucket := l.NewTokenBucket(
		limit,
		refillEvery,
		locker,
		backend,
		clk,
		nil,
	)

	for i := 0; i < 4; i++ {
		wait, err := bucket.Limit(ctx)
		if err != nil {
			assert.ErrorIs(s.T(), err, l.ErrLimitExhausted)
		}
		if wait.Seconds() > 0 {
			clk.Sleep(time.Second) // after a second all keys expired and the initial state was returned, but lastVersion is not cleared
		}
	}
}

checkResponseFromRedis returns error:

got [1 1 OK OK] from redis, expected [3 1 OK OK]

[oskarwojciski]

I have created a PR with proposed solution for that: #30

[oskarwojciski]

Resolved with #30