Trading API: Close Position should have its own Response model.

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Is your feature request related to a problem? Please describe.

ClosePositionResponse is needed because the response can vary on whether there is an open position or not. Furthermore, for non-existing positions, there can be varying responses depending on whether there is an open order for that symbol.

### Describe the solution you'd like.

_No response_

### Describe an alternate solution.

_No response_

### Anything else? (Additional Context)

_No response_