Enhance framework compatibility

[Uralstech]

Overview:
This pull request enhances framework compatibility of LLamaSharp, addressing some issues discussed in #178.

Changes Made:

• Updated preprocessor directives in the LLamaSharp C# project to ensure compatibility with .NET Standard 2.0 and higher and .NET 6.0 and higher.
• Additionally, preprocessor errors have been introduced to provide clear feedback when attempting to target a possibly unsupported framework.

[martindevans]

Thanks for the PR!

I don't think the approach taken here it quite right though. The extension methods covered with #if NETSTANDARD2_0 are usually polyfills for methods which were introduced in later versions of dotnet. That means they should be defined on platforms where those methods don't exist, but must not exist on platforms where those methods already exist.

You could probably use #if !NETSTANDARD2_1 for most of the blocks I would guess?

[Uralstech]

I don't think the approach taken here it quite right though. The extension methods covered with #if NETSTANDARD2_0 are usually polyfills for methods which were introduced in later versions of dotnet. That means they should be defined on platforms where those methods don't exist, but must not exist on platforms where those methods already exist.

You could probably use #if !NETSTANDARD2_1 for most of the blocks I would guess?

I understand. In my previous testing with Unity, I had found EnsureCapacity<T>(this List<T> list, int capacity) is not defined, so I thought it would be better to update all instances of NETSTANDARD2_0.

I'll just have EnsureCapacity with NETSTANDARD2_0 || NETSTANDARD2_1 then!

Edit: I just updated it!

[martindevans]

Thanks for fixing that so quickly, just a couple of other minor nits I spotted in review :)

[martindevans]

Looks good to me! Just waiting for those tests to run and I'll merge it. Thanks very much :)

[Uralstech]

Thank you! You're welcome!