[Patch] Fix balance scheduling (#7611)

### What this PR does / why we need it?
This PR introduces a "balance scheduling" feature, enabled by the
`VLLM_ASCEND_BALANCE_SCHEDULING` environment variable. This feature
adjusts the scheduling logic to better balance the load across
data-parallel workers, preventing a single worker from blocking
scheduling for others. This can improve overall throughput.

Additionally, this PR includes a number of other updates and fixes to
the scheduler, syncing it with a more recent version of the upstream
vLLM scheduler. These changes include:
- Handling for paused scheduler state.
- Support for Mamba block-aligned splits.
- Handling for streaming requests.
- Refinements in preemption logic and resource management (KV cache,
encoder cache).
- General code refactoring for clarity and correctness.

Fixes #

### Does this PR introduce _any_ user-facing change?
Yes, this PR introduces a new feature controlled by the
`VLLM_ASCEND_BALANCE_SCHEDULING` environment variable. When enabled, the
scheduling behavior changes, which could affect performance and request
throughput.

### How was this patch tested?
CI passed. Further testing should be done to validate the performance
and correctness of the new scheduling logic under various workloads,
with and without the feature flag enabled.

Signed-off-by: GDzhu01 <809721801@qq.com>

vllm_ascend/patch/platform/__init__.py

@@ -19,6 +19,7 @@ import os
 import vllm_ascend.patch.platform.patch_distributed  # noqa
 import vllm_ascend.patch.platform.patch_fusion_matcher_compat_ops  # noqa
 import vllm_ascend.patch.platform.patch_kv_cache_interface  # noqa
+from vllm_ascend import envs
 from vllm_ascend.utils import is_310p
 
 if not is_310p():
@@ -31,3 +32,6 @@ import vllm_ascend.patch.platform.patch_torch_accelerator  # noqa
 
 if os.getenv("DYNAMIC_EPLB", "false").lower() in ("true", "1") or os.getenv("EXPERT_MAP_RECORD", "false") == "true":
     import vllm_ascend.patch.platform.patch_multiproc_executor  # noqa
+
+if envs.VLLM_ASCEND_BALANCE_SCHEDULING:
+    import vllm_ascend.patch.platform.patch_balance_schedule  # noqa