refactor linear (#2867)

### What this PR does / why we need it?
The current linear.py has the following issues:

- There is redundant conditional logic in the `comm_group` and `forward`
selection for classes such as `AscendMergedColumnParallelLinear`.

- Inconsistent comm_group selection logic exists among
`AscendMergedColumnParallelLinear`, `AscendColumnParallelLinear`, and
`AscendQKVParallelLinear`.

To address these two issues, this PR encapsulates `comm_group` and
`forward` into classes and extracts the classes selection logic into
common functions. For future additions of custom communication groups or
forward methods, it will only be necessary to extend
`CustomColumnParallelOp` or `CustomRowParallelOp` and add new selection
logic.

### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?


- vLLM version: v0.10.2
- vLLM main:
dd39baf717

---------

Signed-off-by: realliujiaxu <realliujiaxu@163.com>
Co-authored-by: weijinqian0 <weijinqian@huawei.com>

tests/ut/models/test_qwen2_5_vl.py

@@ -295,7 +295,7 @@ class TestAscendQwen2_5_VisionTransformer(PytestBase):
         mock_group.rank_in_group = 0
         mock_group.world_size = 2
         mocker.patch(
-            "vllm_ascend.ops.linear.get_tp_group",
+            "vllm_ascend.ops.linear_op.get_tp_group",
             return_value=mock_group,
         )