string.unpack vararg returns

Nadie ha tomado este issue todavía.

### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

Linux

### What is the issue affecting?

Annotations, Type Checking, Completion

### Expected Behaviour

The current `string.unpack` annotations (for the returns) are as following:

```lua
---@param fmt string
---@param s string
---@param pos? integer
---@return any ...
---@return integer offset
---@nodiscard
function string.unpack(fmt, s, pos) end
```

The function will indeed return any number of `any` returns followed by a single integer return for the new offset. As such you would expect that in the following example code, all of the returns are `any` except the last return be `integer`:

```lua
local a, b, c, d, offset = string.unpack('I2I2I2I2', "some binary data")
```

### Actual Behaviour

Instead of the `a, b, c, d` being typed as `any` and `offset` being typed as `integer`, we instead see that `a` is typed as `any`, `b` is typed as `integer`, and `c, d, offset` are typed as `nil`.

This happen because it is not supported for a function to return a vararg followed by any return; it is always that vararg returns are the last return. Because of that, only the first return is typed as `any` and from there the second `@return` takes.

### Reproduction steps

1. Copy the example code.
2. Hover over each return variable to notice the type.

### Additional Notes

_No response_

### Log File

_No response_

Comienza con la anotación de string.unpack y reproduce el problema en la extensión de Visual Studio Code pasando el cursor sobre cada variable devuelta. Sigue cómo el comprobador de tipos maneja un vararg seguido del retorno del offset. Se considera terminado cuando los valores de unpack están tipados como any y el offset final está tipado como integer.

Escrito por el modelo de indexación a partir del texto del issue.