fix: multi-model routing — each adapter uses own dspy.LM instance

- DSPyLLMAdapter now accepts dspy.LM instead of model string, uses dspy.context(lm=...)
- DSPyJudgeAdapter, DSPyProposerAdapter, DSPySyntheticAdapter each accept and use own LM
- OptimizationConfig gains per-model api_base/api_key_env override fields
- cli/app.py creates separate dspy.LM per adapter with per-model overrides
- New unit tests verify each adapter isolates its LM from global config

Fixes Bug #1 (multi-model config not wired) and Bug #2 (DSPyLLMAdapter ignores model param).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/integration/test_dspy_adapters.py

@@ -16,13 +16,12 @@ def mock_lm() -> dspy.LM:
             {"output": "Mock output response"},
         ]
     )
-    dspy.configure(lm=lm)
     return lm
 
 
 class TestDSPyLLMAdapter:
     def test_execute_returns_response(self, mock_lm: dspy.LM) -> None:
-        adapter = DSPyLLMAdapter(model="openai/gpt-4o-mini")
+        adapter = DSPyLLMAdapter(lm=mock_lm)
         prompt = Prompt(text="Answer the question.")
         result = adapter.execute(prompt, "What is 2+2?")
         assert isinstance(result, str)