Add tests for custom operator implementation correctness

[Kacper-Pietkun]

I added tests for custom ops defined in vllm_gaudi/ops:

• For the tests of ops that are not using cuda kernels - native ops and hpu ops are triggered for the same input and their outputs are compared
• For others tests that are using cuda kernels (so cannot be called with vllm-gaudi plugin) I created separate directory to store some predefined small tensors (to avoid hardcoding them in tests) - weights, inputs and outputs. Such tests run hpu ops with loaded inputs and weights and compare their outputs with the loaded outputs.