[Feature] implement basic framework for batch invariant (#5517)

### What this PR does / why we need it?
This PR implement the basic framework for batch invariant, please see
https://github.com/vllm-project/vllm-ascend/issues/5487.
### Does this PR introduce _any_ user-facing change?
we reuse the function `vllm_is_batch_invariant` in vllm to judge if
batch invariant is enabled.

- vLLM version: v0.13.0
- vLLM main:
45c1ca1ca1
---------
Signed-off-by: Ronald1995 <ronaldautomobile@163.com>
Signed-off-by: Lord_of_Ironhill <suiweiyi@huawei.com>
Signed-off-by: zjchenn <zjchenn@gmail.com>
Signed-off-by: wangx700 <wangxin700@huawei.com>
Co-authored-by: Lord_of_Ironhill <suiweiyi@huawei.com>
Co-authored-by: zjchenn <zjchenn@gmail.com>
Co-authored-by: wangx700 <wangxin700@huawei.com>

.github/workflows/_e2e_test.yaml

@@ -123,6 +123,7 @@ jobs:
           pytest -sv --durations=0 tests/e2e/singlecard/spec_decode/test_v1_spec_decode.py
 
           pytest -sv --durations=0 tests/e2e/singlecard/model_runner_v2/test_basic.py
+          pytest -sv --durations=0 tests/e2e/singlecard/test_batch_invariant.py
 
   e2e-2-cards:
     name: multicard-2