[Example] add flashattention in example and modify ci test

[RuizeYu05]

Description

I add the example of implementing flash attention using allo and modify the CI test to support the testing of my flash attention kernel.

Problems

Implementing flash attention using allo

Proposed Solutions

Add an example to the application of allo

Examples

Checklist

Please make sure to review and check all of these items:

• PR's title starts with a category (e.g. [Bugfix], [IR], [Builder], etc)
• All changes have test coverage (It would be good to provide ~2 different test cases to test the robustness of your code)
• Pass the formatting check locally
• Code is well-documented

[chhzh123]

Thanks for your PR! I think you also need to update the requirements.txt. Check out the CI error

[RuizeYu05]

Yeah I'm currently fixing it.

[Copilot]

Pull request overview

Adds a FlashAttention example kernel implemented in Allo and wires it into CI so the example is exercised during PR runs.

Changes:

• Added a FlashAttention Allo schedule/kernel implementation (get_scheduled_flash_attention).
• Added a Python testbench that builds/runs the kernel and compares against a NumPy golden reference.
• Updated GitHub Actions workflow to execute the FlashAttention testbench.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
examples/flashattention/test_flash.py	Testbench that computes a golden attention output and validates the Allo-generated kernel (plus optional Vitis HLS synthesis).
examples/flashattention/flash_Atten.py	Allo implementation/schedule for a tiled FlashAttention-style attention computation.
.github/workflows/config.yml	Adds a CI step to run the FlashAttention testbench.

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[chhzh123]

Can you fix Copilot's suggestions (if they are valid)? Also, it'd be good to attach your performance results in the PR description

[Copilot]

Copilot review overview

🟡 Changes recommended

Public parameter validation and unconditional HLS code-generation coverage need correction.

Review effort: Balanced
Findings: 1

Open (1)

• Guard only HLS lowering, not the entire Vitis-target build · New

[Fangtangtang]

Hi @RuizeYu05, sorry for the very delayed review.
Shall we put falshattention in this PR and MHA in #581 under the same directory named "attention"? It would also be great to add a README under this directory describing the kernels (e.g., algorithm/dataflow/performance results).
Also, the current CI only runs the simulator. Could you add this example to .github/workflows/fpga_weekly.yml to enable tests on hls?