fix: always return ModelSettings from _build_model_settings #656

Job	Run time
server-ai-optimization-windows (3.10)	19s
server-ai-openai-windows (3.10)	24s
server-ai-openai-windows (3.11)	28s
server-ai-openai-windows (3.12)	25s
server-ai-openai-windows (3.13)	25s
server-ai-openai-windows (3.14)	26s
server-ai-linux (3.10)	16s
server-ai-optimization-windows (3.12)	17s
server-ai-optimization-windows (3.13)	19s
server-ai-linux (3.11)	20s
server-ai-linux (3.14)	17s
server-ai-openai-linux (3.12)	25s
server-ai-linux (3.12)	16s
server-ai-langchain-linux (3.10)	23s
server-ai-optimization-windows (3.14)	26s
server-ai-openai-linux (3.11)	24s
server-ai-linux (3.13)	16s
server-ai-openai-linux (3.10)	27s
server-ai-windows (3.12)	20s
server-ai-windows (3.11)	23s
server-ai-windows (3.10)	24s
server-ai-optimization-linux (3.12)	13s
server-ai-langchain-linux (3.11)	20s
server-ai-windows (3.14)	27s
server-ai-openai-linux (3.13)	24s
server-ai-langchain-linux (3.12)	22s
server-ai-windows (3.13)	22s
server-ai-langchain-linux (3.13)	20s
server-ai-langchain-windows (3.11)	29s
server-ai-optimization-linux (3.14)	15s
server-ai-optimization-linux (3.11)	14s
server-ai-langchain-windows (3.12)	29s
server-ai-optimization-linux (3.10)	14s
server-ai-langchain-windows (3.13)	27s
server-ai-langchain-windows (3.10)	45s
server-ai-openai-linux (3.14)	29s
server-ai-optimization-windows (3.11)	27s
server-ai-optimization-linux (3.13)	14s
server-ai-langchain-windows (3.14)	46s
server-ai-langchain-linux (3.14)	19s
	15m 16s

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