Fix connection leak in fetchURL

[mclaughlin-thomas]

The function fetchURL() only reads the response status and Location header -- it does not touch the body. SetDoNotParseResponse(true) tells resty not to drain or close the body for us, transferring that responsibility to the caller.

// SetDoNotParseResponse method instructs Resty not to parse the response body automatically.
// Resty exposes the raw response body as [io.ReadCloser]. If you use it, do not
// forget to close the body, otherwise, you might get into connection leaks, and connection
// reuse may not happen.
//
// NOTE: [Response] middlewares are not executed using this option. You have
// taken over the control of response parsing from Resty.
func (c *Client) SetDoNotParseResponse(notParse bool) *Client {
	c.notParseResponse = notParse
	return c
}

Since we never close it, the body and its underlying socket stay open.

Removing the option lets resty handle body cleanup on its normal path.
No behavior change for callers; existing tests still pass.