[refactor] refactor excute_model and _dymmy_run method (#6043)

### What this PR does / why we need it?
The structure of the `excute_model` and `_dymmy_run` methods in
NPUModelRunner differs greatly from that in GPUModelRunner.
Achieve alignment with GPUModelRunner:
Split the `_prepare_inputs` method into `_prepare_inputs`,
`_determine_batch_execution_and_padding`, `_build_attention_metadata`,
and `_preprocess`.
Modify `_generate_process_reqs_hidden_states` to `_model_forward`.
Align the implementation of the `postprocess` phase

**Related-RFC**: https://github.com/vllm-project/vllm-ascend/issues/5449

**Co-authored-by**: @zhenwenqi2024 
### Does this PR introduce _any_ user-facing change?
no
### How was this patch tested?

- vLLM version: v0.13.0
- vLLM main:
d68209402d

---------

Signed-off-by: Wang Kunpeng <1289706727@qq.com>
Signed-off-by: gcanlin <canlinguosdu@gmail.com>
Signed-off-by: zhenwenqi2024 <zhenwenqi_2022@qq.com>
Co-authored-by: gcanlin <canlinguosdu@gmail.com>
Co-authored-by: zhenwenqi2024 <zhenwenqi_2022@qq.com>

tests/ut/worker/test_pcp_manager.py

@@ -123,6 +123,7 @@ def test_update_tokens_for_pcp_basic(tokens, num_reqs, num_computed_tokens,
     vllm_config = MagicMock()
     vllm_config.model_config = MagicMock()
     vllm_config.speculative_config.num_speculative_tokens = 0
+    vllm_config.scheduler_config.max_num_seqs = 1000
 
     pcp_manager = PCPManager(pcp_world_size=pcp_size,
                              pcp_rank=0,