Introduce Span<T> to StunMessage

[longfin]

Context

After C# 7.2 & System.Memory, Span<T> was introduced to reduce heap allocation. It would be great if we can apply it to StunMessage's parsing process to improve performance.

Tips

• Because .netstandard2.0 doesn't support Stream.ReadAsync(Memory<T>) and Stream.ReadAsync(Span<T>), you'll need to branch through a preprocessor. Then this MSDN docs will be helpful.

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[moreal]

As you said, C# 7.2 introduced Memory<T>, Span<T> and they help memory management effect But it seems not to support Stream.ReadAsync(Memory<T>), Stream.ReadAsync(Span<T>). There is only Stream.ReadAsync(byte[]) in .netstandard2.0.
Futrhermore, Libplanet target multiple frameworks, .netcoreapp3.0 and .netstandard2.0.

Though it was tried, but it couldn't be applied sadly because of them.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.

[OnedgeLee]

@longfin May I close this issue?
As @moreal mentioned, seems like dotnet does not support Stream.ReadAsync(Span<T>) at all. (only Stream.ReadAsync(Memory<T>) is available.)

[longfin]

Sure.