More optimized remainder calculation

[lechu445 (lechu445)]

Instead of division then remainder operation, used Math.DivRem which handles it in a more optimized way. It uses only a single division, multiplication, and subtraction instead of two divisions. Moreover, in the future, it can be even more optimized using intrinsics.

See:
dotnet/runtime#5213 (comment)

[Paulo Morgado (paulomorgado)]

It would be nice if this PR was acompanied by benchmarks.

[lechu445 (lechu445)]

before:

|    Method |     Mean |   Error |   StdDev |
|---------- |---------:|--------:|---------:|
| WriteByte | 184.0 ms | 3.64 ms |  5.34 ms |
| WriteSpan | 366.3 ms | 7.07 ms | 12.00 ms |

after:

|    Method |     Mean |   Error |   StdDev |
|---------- |---------:|--------:|---------:|
| WriteByte | 115.5 ms | 2.30 ms |  3.23 ms |
| WriteSpan | 319.7 ms | 6.28 ms | 11.49 ms | 

code:

public class Test
{
    private RecyclableMemoryStream subject;
    private readonly byte[] bytes = new byte[] { 1, 2, 3, 4, 5, 6 };

    [IterationSetup]
    public void IterationSetup()
    {
        var manager = new RecyclableMemoryStreamManager();
        this.subject = new RecyclableMemoryStream(manager);
    }

    [Benchmark]
    public void WriteByte()
    {
        for (int i = 0; i < 10_000_000; i++)
        {
            this.subject.WriteByte(1);
        }
    }

    [Benchmark]
    public void WriteSpan()
    {
        for (int i = 0; i < 10_000_000; i++)
        {
            this.subject.Write(bytes.AsSpan());
        }
    }
}

[Paulo Morgado (paulomorgado)]

I was thinking more in the lines of:

public class Benchmarks
{
	[Benchmark(Baseline = true)]
	public (long quocient, long remainder) DivAndMod() => (4000L / 1024L, 4000L % 1024L);

	[Benchmark]
	public (long quocient, long remainder) MathDivRem() => Math.DivRem(4000L, 1024L);
}

Method	Mean	Error	StdDev	Ratio	RatioSD
DivAndMod	0.2267 ns	0.0092 ns	0.0077 ns	1.00	0.00
MathDivRem	0.0607 ns	0.0221 ns	0.0271 ns	0.25	0.12