nki-samples updates for NeuronSDK release 2.21

[aws-qieqingy]

Issue #, if available:

nki-samples updates associated with NeuronSDK release 2.21.

See detailed release notes at: https://awsdocs-neuron.readthedocs-hosted.com/en/latest/release-notes/index.html#neuron-2-21-0-12-20-2024

Description of changes:

1. Use the new neuronxcc.nki.jit decorator for kernels. The old decorator torch_neuronx.nki_jit is deprecated, and will be eventually removed.
2. Provide two samples for the new direct allocation feature. See the direct allocation developer guide for details: https://awsdocs-neuron.readthedocs-hosted.com/en/latest/general/nki/nki_direct_allocation_guide.html
3. Restructure the source code and added Github workflow to run simulation tests
4. Misc tests and documentation improvements

Testing:

Please see detailed unit test requirements in the CONTRIBUTING.md

• The change is covered by numeric check using nki.baremetal
• The change is covered by performance benchmark test using nki.benchmark
• The change is covered by end-to-end integration test

Pull Request Checklist

• I have filled in all the required field in the template
• I have tested locally that all the tests pass
• By submitting this pull request, I confirm that my contribution is made under the terms of the MIT-0 license.