[Platform] Enable ARM-only CPU binding with NUMA-balanced A3 policy and update docs/tests (#6686)

### What this PR does / why we need it?

- Keeps enable_cpu_binding default on, but skips binding on non‑ARM CPUs
inside bind_cpus, with a clear log.
- Uses a table-driven binding policy: A3 uses NUMA‑balanced binding;
other device types use NUMA‑affinity binding.
- Updates docs to reflect the exact behavior and adds/updates unit tests
for the new logic.

### Does this PR introduce _any_ user-facing change?

- Yes. CPU binding is now enabled by default via additional_config, and
documented in the user guide.
- CPU binding behavior differs by device type (A3 vs. others).

### How was this patch tested?

Added/updated unit tests:

test_cpu_binding.py
1.   test_binding_mode_table covers A2 vs A3 binding mode mapping.
2. test_build_cpu_pools_fallback_to_numa_balanced covers fallback when
affinity info is missing.
3. TestBindingSwitch.test_is_arm_cpu covers ARM/x86/unknown arch
detection.
4.   test_bind_cpus_skip_non_arm covers non‑ARM skip path in bind_cpus.

test_worker_v1.py
1. Updated mocks for enable_cpu_binding default True to align with new
config default.

- vLLM version: v0.14.1
- vLLM main: d7de043

---------

Signed-off-by: chenchuw886 <chenchuw@huawei.com>
Co-authored-by: chenchuw886 <chenchuw@huawei.com>

requirements.txt

@@ -9,6 +9,7 @@ pybind11
 pyyaml
 scipy
 pandas
+psutil
 setuptools>=64
 setuptools-scm>=8
 torch==2.9.0