feat(client): add generic type parameter to predict() method

[majiayu000]

Summary

• Add generic type parameter to PredictReturn<T> for type-safe data access
• Add generic type parameter to PredictFunction for typed predictions
• Add SubmitIterable interface methods (next, throw, return) for proper iterator typing

This allows users to call client.predict<MyType>() and get typed data:

type MyResponse = { text: string; confidence: number };
const result = await client.predict<MyResponse>("/predict", [input]);
// result.data is now typed as MyResponse instead of unknown
console.log(result.data.text); // TypeScript knows this is a string

Test plan

• Added typing tests to verify generic functionality
• All existing client tests pass
• Build succeeds with proper type generation

Fixes #5462

Signed-off-by: majiayu000 [email protected]