marketcalls/openalgo.NET ? reverse-engineered prompt

Build me a clean C# SDK for the OpenAlgo trading API that I can use from a .NET 6, 7, or 8 app.

I want to create a client with an API key and host URL, then call methods for things like placing market and limit orders, smart orders that take position size into account, and options orders for NIFTY style contracts. Please include both sync and async versions where it makes sense, and make the responses easy to work with so I can print things like status, order id, symbol, and underlying price. It should feel simple to use from a console app or any normal C# project, with good defaults for common fields but still let me override them when needed.

If there are any details that depend on the latest OpenAlgo API behavior, look up the current docs online if you need to. Also add a few small usage examples and basic tests so I can see it working right away.