Reduces heap allocations for the some byte[] uses

[jacobslusser]

Profiling reveals that creation of byte[4] arrays are our most common heap objects. Many of these come from reading integers from the byte stream where we allocate a small byte[4] or byte[8] array and then convert it to a 32 or 64-bit integer.

Results from a simple test of using the SftpClient to upload and download some files:

Before: when byte[] arrays were created for each integer read

After: when byte[] are allocated and read from the stack

Changes

• Creates a new SshDataStream.ReadBytes overload that supports Span<byte> for .NET Standard 2.1+ and .NET 6+ targets.
• Updates SshDataStream.ReadUInt32 and SshDataStream.ReadUInt64 to read onto the stack and use newer BinaryPrimitives class for integer conversion for .NET Standard 2.1+ and .NET 6+ targets.
• Updates SshData.ReadUInt32 and SshData.ReadUInt64 to use the existing stream methods to avoid another temporary buffer.

[Rob-Hague]

Funny, I had very similar changes in #1138 🙂 Feel free to cherry-pick some of those, or otherwise this looks good to me

[jacobslusser]

Funny, I had very similar changes in #1138 🙂 Feel free to cherry-pick some of those, or otherwise this looks good to me

@Rob-Hague wow, your changes are more than a little similar. At one point I had even ported the ReadExactly just as you had but decided instead to follow our existing pattern. I will definitely look at merging the others.

Why didn't you ever merge this?

[Rob-Hague]

I think I wanted to justify it with some profiling like you did, but got stuck into some other work

[WojciechNagorski]

I will merge any optimization if it has justify as goof as this PR 😃. #1138 was a draft.

[WojciechNagorski]

The 2023.0.1 version has been released to Nuget: https://www.nuget.org/packages/SSH.NET/2023.0.1