feat(ai): add strictResponsesPairing for Azure OpenAI Responses API

Split OpenAICompat into OpenAICompletionsCompat and OpenAIResponsesCompat
for type-safe API-specific compat settings. Added strictResponsesPairing
option to suppress orphaned reasoning/tool calls on incomplete turns,
fixing 400 errors on Azure's Responses API which requires strict pairing.

Closes #768

packages/ai/test/total-tokens.test.ts

@@ -155,8 +155,10 @@ describe("totalTokens field", () => {
 			"gpt-4o-mini - should return totalTokens equal to sum of components",
 			{ retry: 3, timeout: 60000 },
 			async () => {
+				const { compat: _compat, ...baseModel } = getModel("openai", "gpt-4o-mini")!;
+				void _compat;
 				const llm: Model<"openai-completions"> = {
-					...getModel("openai", "gpt-4o-mini")!,
+					...baseModel,
 					api: "openai-completions",
 				};