refactor(llm_clients): build the client keyword arguments in llm_clients

- build_llm_kwargs(config) replaces the graph's _get_provider_kwargs, with the retry and token coercion beside it

tests/test_llm_max_tokens.py

@@ -13,7 +13,7 @@ import importlib
 import pytest
 
 import tradingagents.default_config as default_config_module
-from tradingagents.graph.trading_graph import TradingAgentsGraph, _coerce_max_tokens
+from tradingagents.llm_clients.factory import _coerce_max_tokens, build_llm_kwargs
 
 # --- coercion / validation -------------------------------------------------
 
@@ -46,15 +46,10 @@ def test_coerce_rejects_non_integers(bad):
 
 # --- forwarding into provider kwargs (right key per provider) --------------
 
-def _bare_graph(config):
-    g = object.__new__(TradingAgentsGraph)
-    g.config = config
-    return g
-
 
 @pytest.mark.unit
 def test_not_forwarded_when_unset():
-    kwargs = _bare_graph({"llm_provider": "openai", "max_tokens": None})._get_provider_kwargs()
+    kwargs = build_llm_kwargs({"llm_provider": "openai", "max_tokens": None})
     assert "max_tokens" not in kwargs
     assert "max_output_tokens" not in kwargs
 
@@ -62,7 +57,7 @@ def test_not_forwarded_when_unset():
 @pytest.mark.unit
 @pytest.mark.parametrize("provider", ["openai", "anthropic", "deepseek", "openai_compatible"])
 def test_forwarded_as_max_tokens_for_non_google(provider):
-    kwargs = _bare_graph({"llm_provider": provider, "max_tokens": 8192})._get_provider_kwargs()
+    kwargs = build_llm_kwargs({"llm_provider": provider, "max_tokens": 8192})
     assert kwargs["max_tokens"] == 8192
     assert "max_output_tokens" not in kwargs
 
@@ -70,21 +65,21 @@ def test_forwarded_as_max_tokens_for_non_google(provider):
 @pytest.mark.unit
 def test_forwarded_as_max_output_tokens_for_google():
     # Gemini's kwarg name differs; forwarding plain max_tokens would be rejected.
-    kwargs = _bare_graph({"llm_provider": "google", "max_tokens": 8192})._get_provider_kwargs()
+    kwargs = build_llm_kwargs({"llm_provider": "google", "max_tokens": 8192})
     assert kwargs["max_output_tokens"] == 8192
     assert "max_tokens" not in kwargs
 
 
 @pytest.mark.unit
 def test_env_string_is_coerced():
-    kwargs = _bare_graph({"llm_provider": "openai", "max_tokens": "4096"})._get_provider_kwargs()
+    kwargs = build_llm_kwargs({"llm_provider": "openai", "max_tokens": "4096"})
     assert kwargs["max_tokens"] == 4096
 
 
 @pytest.mark.unit
 def test_invalid_value_fails_loudly():
     with pytest.raises(ValueError):
-        _bare_graph({"llm_provider": "openai", "max_tokens": 0})._get_provider_kwargs()
+        build_llm_kwargs({"llm_provider": "openai", "max_tokens": 0})
 
 
 # --- client-side allowlists carry the kwarg --------------------------------