[GenAI] pack GenAI core package

[LittleLittleCloud]

We are excited to review your PR.

So we can do the best job, please check:

• There's a descriptive title that will make sense to other developers some time from now.
• There's associated issues. All PR's should have issue(s) associated - unless a trivial self-evident change such as fixing a typo. You can use the format Fixes #nnnn in your description to cause GitHub to automatically close the issue(s) when your PR is merged.
• Your change description explains what the change does, why you chose your approach, and anything else that reviewers should know.
• You have included any necessary tests in the same PR.

#7169

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 28 lines in your changes missing coverage. Please review.

Project coverage is 68.78%. Comparing base (817a77f) to head (ad6dc64).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Microsoft.ML.GenAI.LLaMA/LlamaForCausalLM.cs	33.33%	20 Missing ⚠️
...st/Microsoft.ML.GenAI.LLaMA.Tests/LLaMA3_2Tests.cs	77.77%	3 Missing and 1 partial ⚠️
src/Microsoft.ML.GenAI.LLaMA/LlamaConfig.cs	66.66%	0 Missing and 2 partials ⚠️
src/Microsoft.ML.GenAI.LLaMA/Module/LlamaModel.cs	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7246      +/-   ##
==========================================
- Coverage   68.78%   68.78%   -0.01%     
==========================================
  Files        1461     1462       +1     
  Lines      272208   272261      +53     
  Branches    28168    28176       +8     
==========================================
+ Hits       187250   187278      +28     
- Misses      77720    77744      +24     
- Partials     7238     7239       +1     

Flag	Coverage Δ
Debug	68.78% <50.00%> (-0.01%)	⬇️
production	63.29% <36.84%> (-0.01%)	⬇️
test	89.04% <77.77%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/Microsoft.ML.GenAI.LLaMA/LlamaConfig.cs	91.52% <66.66%> (-2.82%)	⬇️
src/Microsoft.ML.GenAI.LLaMA/Module/LlamaModel.cs	18.55% <0.00%> (-0.20%)	⬇️
...st/Microsoft.ML.GenAI.LLaMA.Tests/LLaMA3_2Tests.cs	77.77% <77.77%> (ø)
src/Microsoft.ML.GenAI.LLaMA/LlamaForCausalLM.cs	17.64% <33.33%> (+3.61%)	⬆️

... and 7 files with indirect coverage changes