Improve configs - TokenizerPoolConfig + DeviceConfig (#16603)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/test_config.py

@@ -1,14 +1,36 @@
 # SPDX-License-Identifier: Apache-2.0
 
-from dataclasses import asdict
+from dataclasses import MISSING, Field, asdict, dataclass, field
 
 import pytest
 
-from vllm.config import ModelConfig, PoolerConfig
+from vllm.config import ModelConfig, PoolerConfig, get_field
 from vllm.model_executor.layers.pooler import PoolingType
 from vllm.platforms import current_platform
 
 
+def test_get_field():
+
+    @dataclass
+    class TestConfig:
+        a: int
+        b: dict = field(default_factory=dict)
+        c: str = "default"
+
+    with pytest.raises(ValueError):
+        get_field(TestConfig, "a")
+
+    b = get_field(TestConfig, "b")
+    assert isinstance(b, Field)
+    assert b.default is MISSING
+    assert b.default_factory is dict
+
+    c = get_field(TestConfig, "c")
+    assert isinstance(c, Field)
+    assert c.default == "default"
+    assert c.default_factory is MISSING
+
+
 @pytest.mark.parametrize(
     ("model_id", "expected_runner_type", "expected_task"),
     [