Optimize FIFOSet

[erikzhang]

Closes #1382, closes #1389

@eryeer Can you test this?

[eryeer]

Closes #1382, closes #1389

@eryeer Can you test this?

Sure, I'll test it soon.

[eryeer]

Using the same test code as which is used in #1382 .
The result is:

Add timespan: 6.4464343s
except with timespan: 0.0744838s
contains with timespan: 0.0001441s result: False
contains with timespan: 2E-07s result: True

Faster than original FIFOSet but slower than #1389

Below attaches the test code:

        [TestMethod]
        public void TestFIFOSet()
        {
            Stopwatch stopwatch = new Stopwatch();
            var bucket = new FIFOSet<int>(150_000);
            stopwatch.Start();
            for (int i = 1; i <= 550_000; i++)
            {
                bucket.Add(i);
            }
            stopwatch.Stop();
            Console.WriteLine($"Add timespan: {stopwatch.Elapsed.TotalSeconds}s");
            stopwatch.Reset();
            var items = new int[10000];
            var value = 550_000;
            for (int i = 0; i <= 9999; i++)
            {
                items[i] = value;
                value -= 50;
            }
            stopwatch.Start();
            bucket.ExceptWith(items);
            stopwatch.Stop();
            Console.WriteLine($"except with timespan: {stopwatch.Elapsed.TotalSeconds}s");
            stopwatch.Reset();

            stopwatch.Start();
            var ret = bucket.Contains(140_000);
            stopwatch.Stop();
            Console.WriteLine($"contains with timespan: {stopwatch.Elapsed.TotalSeconds}s result: {ret}");
            stopwatch.Reset();

            stopwatch.Start();
            ret = bucket.Contains(545_001);
            stopwatch.Stop();
            Console.WriteLine($"contains with timespan: {stopwatch.Elapsed.TotalSeconds}s result: {ret}");
            stopwatch.Reset();
        }

[vncoelho]

@eryeer, @erikzhang, looking at the results here: #1389 (comment)

I believe it will be better to move to the "HashSet", a little more complex (almost as in the original, but considerably faster).

Nice job, @eryeer, as always.