Improve Code Quality

[iamcarbon]

This PR:

• Drops unsupported .NET frameworks. All .NET frameworks < 4.6.2 have gone out of support.
  https://learn.microsoft.com/en-us/lifecycle/products/microsoft-net-framework
• Cross targets .NET8.0
• Updates LangVersion to 12
• Utilizes statically initialized data (allocation free)
• Add System.Memory dependency to utilize ReadOnlySpan and utf-8 literals
• Add Microsoft.Bcl.HashCode dependency and utilizes HashCode.Combine
• Replaces EmptyArray with Array.Empty
• Add various missing braces
• Utilized vectorized SequenceEqual method
• Uses BinaryPrimitives to read big endian integers

[iamcarbon]

@ EliotJones Ready for review / feedback.

[BobLd]

@EliotJones I did a quick review and it looks good to me.

I think it's about time we drop out of support framework, so this is a great opportunity to do so

[Numpsy]

Purely on the subject of TFMs

1. I think adding a .NET 4.7.1 target would remove the System.ValueTuple NuGet dependency for consumers of that version (e.g. Serilog targets 4.6.2 and 4.7.1 for that reason)
2. If the main lib is built as both .NET 6.0 and 8.0 then maybe the unit tests should be as well?

[iamcarbon]

With net6.0 going out of support in November (of this year), what do we think about bumping the testing target to .NET8.0 as well? .NET8.0 will be supported until November 2026.

Purely on the subject of TFMs

1. I think adding a .NET 4.7.1 target would remove the System.ValueTuple NuGet dependency for consumers of that version (e.g. Serilog targets 4.6.2 and 4.7.1 for that reason)
2. If the main lib is built as both .NET 6.0 and 8.0 then maybe the unit tests should be as well?

• Agreed. I bumped the net47 target to net471 (matching Serilog). The System.ValueTuple dependency is only needed on net462 now.
• I added net8.0 to the testing targets. We should consider dropping the net6.0 test target in November when it goes out of support, to reduce build overhead.

[BobLd]

@iamcarbon I think it's safe to drop the net6.0 test target for the net8.0

Also, the tests are now failing... might be related, I think there's an issue in the yaml change: seems like it cannot target 2 different dotnet versions (only target net8.0 then?)

As a side note, I think it's better to not make this PR too much bigger for ease of review. The great job you did with span opens a lot of optimisation which can be done in later PRs

I'll let @EliotJones give his opinion on obsolete framework version. I need to review the changes more thoroughly but I'd be happy to merge the PR as it is I think

[EliotJones]

Thanks for the changes