VivadoAccelerator complete build test

[marco66colombo]

Description

This is a draft PR and a CI experiment.

Goal: verify that we can run the end-to-end VivadoAccelerator build flow in CI for at least one Keras API test.

This is a first step toward extending CI coverage to analogous end-to-end flows for Vitis backends, building on:

• Vitis Unified Backend #1376
• Vitis Accelerator IP Flow #1134

For now, this PR only checks one case so we can validate the workflow.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• Documentation update
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• A new research paper code implementation
• Other (Specify): CI/testing workflow experiment (draft)

Tests

This PR is intentionally limited to one small CI synthesis test.

What is tested:

• New test file introduced in this PR: test/pytest/test_keras_api_vivadoacc.py.
• VivadoAccelerator build flow on one adapted test case (test_dense) from test_keras_api.

Test Configuration:

• Backend: VivadoAccelerator
• Test file: test/pytest/test_keras_api_vivadoacc.py (adapted from test_keras_api)

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have installed and run pre-commit on the files I edited or added.
• I have added tests that prove my fix is effective or that my feature works.

[nghielme]

I'd set it to True