.net 6 target for manged GenAI

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### Describe the issue

Hi , I was able to -somehow - add GenAI to unity back then, but when testing new futures with mulitmodal APIs , it failed to load the dlls, due to some restriction on the build target as far as I know, unity support the standard 2.1 for most parts, and most of .net 6 BCL [not sure yet]
now when I try to update my project, it failed with this message:

and sometimes, it failed to load the managed AI .dll completely (even if I can reference some namespace)

so my question is can I or anyone who would like to help building form source or try to port these to compatible unity runtime ? thanks .

### To reproduce

download the mangedGenAI dlls , and load it to unity .

script works just fine but at runtime it failed even if I change the scripting backend

### Urgency

_No response_

### Platform

Windows

### OS Version

0

### ONNX Runtime Installation

Released Package

### ONNX Runtime Version or Commit ID

0.12.0

### ONNX Runtime API

C#

### Architecture

X64

### Execution Provider

Other / Unknown

### Execution Provider Library Version

_No response_

Start by downloading the managed GenAI DLLs and reproducing the runtime failure in Unity on Windows x64. Check the reported behavior with the C# API, ONNX Runtime 0.12.0 released package, and each available scripting backend. Done would mean establishing whether the DLLs can run on Unity's supported runtime or defining the compatibility work needed for a port.

Written by the indexing model from the issue text.