feat: add runnable CI example for OpenCL/VCL backend

[ulises-jeremias]

examples/vtl_opencl_vcl_support only has main_not_ci.v (excluded from CI).
The OpenCL backend is tested only via manual runs.

Task

Add examples/vtl_opencl_vcl_support/main.v that:

1. Checks for OpenCL device availability
2. Skips with a clean exit if no device
3. Runs a small tensor operation if device available
4. Wire into .github/workflows/ci.yml

Files

• examples/vtl_opencl_vcl_support/main.v
• .github/workflows/ci.yml