Fix `io.ably.nuspec` with minimum and required TFM

[sacOO7]

• Related to Upgrade deprecated xamarin projects to .NET #1281
• Currently, io.ably.nuspec has tons of platforms, we can reduce them to just two netstandard2.0 and net6.0 if above issue is addressed.
• This will also remove need to maintain separate io.ably.nuspec file ( optional ), thought this is recommended to have clear vision of dependencies across projects. Removing io.ably.nuspec will require publishing deltacodec as a separate dependency.

┆Issue is synchronized with this Jira Task by Unito

[sacOO7]

We should also check if existing netframework project file can be made compatible with new dotnet style format.
It will help us restore and clean project in cross platform scenario.
Also, deltaCodec can be added a nuget dependency for the same, instead of merging it using ilRepackHelper

[sacOO7]

For now, we will need three types of projects
netframework, netstandard and net6.0

[sacOO7]

For now, we will need three types of projects netframework, netstandard and net6.0

This is similar to https://www.nuget.org/packages/MessagePack#dependencies-body-tab

[sacOO7]

• Currently, MAUI compilation for iOS in release mode in fail because iOS needs AOT compilation of all dependencies
• See issue -> Export iOS - newtonsoft parse JSON - Unable to find default constructor for System.Collections.Generic.List #1295
• As per gemini =>

Compatibility Details

Android: Newtonsoft.Json typically works in both debug (JIT) and release (JIT or AOT) modes without significant issues.

iOS: This is where the issues arise. iOS requires full AOT compilation, which limits dynamic code generation (like Reflection.Emit). Newtonsoft.Json heavily uses reflection and some dynamic code generation under the hood for serialization and deserialization, which causes problems in a pure AOT environment.

Known Issues on iOS (Release Builds)

While the library itself targets compatible frameworks like .NET Standard, using it in an AOT environment like an iOS release build can lead to runtime errors, such as JsonSerializationException or ExecutionEngineException, because the compiler cannot see all the code paths accessed via reflection.

A common symptom is that the app works perfectly in Debug mode (which uses an interpreter and allows JIT) but crashes in Release mode (which is AOT-compiled).

[sacOO7]

Seems, we can specify different dependencies for iOS targets in NuGet package by utilizing Target Framework Monikers (TFMs) within the .nuspec file's section and organizing your library's output by TFM in the lib folder.
This approach is necessary because a standard net6.0 dependency group may not fully satisfy the unique AOT requirements of net6.0-ios.

Modifying the .nuspec File

You can add a specific for net6.0-ios (or a specific version like net6.0-ios13.0) and omit or change the Newtonsoft.Json dependency for that specific target.
Here is how you would modify your nuspec file:

<dependencies>
    <!-- Dependencies for generic net6.0 (e.g., Android JIT, Windows, etc.) -->
    <group targetFramework="net6.0">
        <dependency id="System.Threading.Channels" version="4.6.0" />
        <dependency id="Newtonsoft.Json" version="13.0.1" />
    </group>

    <!-- Dependencies for net6.0-ios (AOT environment) -->
    <group targetFramework="net6.0-ios">
        <dependency id="System.Threading.Channels" version="4.6.0" />
        <!-- Intentionally omit Newtonsoft.Json here, assuming the iOS specific library handles serialization differently, 
             perhaps using System.Text.Json internally or an AOT-compatible version if one exists (which is unlikely). -->
    </group>
</dependencies>

Structuring the Package Files

You must also structure your package's lib folder to contain the correct DLLs for each TFM. When packing from an SDK-style project, NuGet automatically handles the folder structure if the project is multi-targeted.
You would need to ensure your source project generates two separate build outputs and include them accordingly in the nuspec file:

<files>
    <!-- Files for generic net6.0 (uses standard Newtonsoft.Json) -->
    <file src="..\src\IO.Ably.NETStandard20\bin\$configuration$\net6.0\IO.Ably.*" target="lib\net6.0" />

    <!-- Files for net6.0-ios (uses AOT-compatible serialization internally) -->
    <file src="..\src\IO.Ably.NETStandard20\bin\$configuration$\net6.0-ios\IO.Ably.*" target="lib\net6.0-ios" />
</files>

[sacOO7]

This will need merging Newtonsoft.Json.dll from lib/AOT and merging it with netstandard2.0/IO.Ably.dll as a part of build process using ILRepack. Then it will be put into net6.0-ios\. It will picked up .nuspec for further processing.