[Core][Misc] Clean up ProfileExecuteDuration (#6461)

### What this PR does / why we need it?
This PR removes the custom `ProfileExecuteDuration` utility and its
usages across the codebase. This utility was used for profiling
execution duration of different stages in the inference process. It is
replaced by the standard `vllm.v1.utils.record_function_or_nullcontext`,
which integrates with PyTorch's profiler.

This change simplifies the code by removing a custom implementation in
favor of an upstream utility, improving maintainability. Associated
documentation and tests for `ProfileExecuteDuration` are also removed.

### Does this PR introduce _any_ user-facing change?
`VLLM_ASCEND_MODEL_EXECUTE_TIME_OBSERVE` env is removed now.

### How was this patch tested?
CI passed. The changes are a cleanup and replacement with a standard
utility. Existing tests cover the functionality. The removed feature had
its own tests which are also removed.

Related RFC: #5304

- vLLM version: v0.14.1
- vLLM main:
dc917cceb8

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

vllm_ascend/spec_decode/mtp_proposer.py

@@ -10,6 +10,7 @@ from vllm.v1.attention.backends.utils import CommonAttentionMetadata
 from vllm.v1.core.sched.output import SchedulerOutput
 from vllm.v1.sample.metadata import SamplingMetadata
 from vllm.v1.spec_decode.eagle import PADDING_SLOT_ID
+from vllm.v1.utils import record_function_or_nullcontext
 
 from vllm_ascend.ascend_forward_context import set_ascend_forward_context
 from vllm_ascend.attention.attention_v1 import AscendAttentionState
@@ -17,7 +18,7 @@ from vllm_ascend.attention.utils import AscendCommonAttentionMetadata
 from vllm_ascend.compilation.acl_graph import ACLGraphWrapper
 from vllm_ascend.ops.rotary_embedding import get_cos_and_sin_mla
 from vllm_ascend.spec_decode.eagle_proposer import EagleProposer
-from vllm_ascend.utils import ProfileExecuteDuration, lmhead_tp_enable, vllm_version_is
+from vllm_ascend.utils import lmhead_tp_enable, vllm_version_is
 
 
 class MtpProposer(EagleProposer):
@@ -311,7 +312,7 @@ class MtpProposer(EagleProposer):
                     batch_descriptor=batch_descriptor,
                     num_actual_tokens=num_tokens,
                     is_draft_model=True):
-                with ProfileExecuteDuration().capture_async('mtp_forward'):
+                with record_function_or_nullcontext('mtp_forward'):
                     model_kwargs = {}
                     model_kwargs["attn_metadata"] = attn_metadata
                     input_ids = self.input_ids[:num_input_tokens]