Custom __pairs expects only 1 return value

還沒有人認領這個 Issue。

### 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?

Type Checking

### Expected Behaviour

I expected no warnings

### Actual Behaviour

There is a redundant return value warning

### Reproduction steps

Here's an example where string paths are transformed to their package.loaded value

```lua
local imports = {
mod1 = "src.mod1",
mod2 = "src.mod2"
}

return setmetatable({}, {
__pairs = function(_)
local iter = pairs(imports)

local newiter = function (table, index)
local k, path = iter(table, index)

return k, package.loaded[path]
end

--- LuaLS is wrong here
---@diagnostic disable-next-line:redundant-return-value
return newiter, imports, nil
end
})
```

### Additional Notes

https://www.lua.org/pil/7.3.html

### Log File

_No response_

在 Linux 上使用提供的 setmetatable 和 __pairs 範例，重現 LuaLS Visual Studio Code extension 中的警告。先從 __pairs 的型別檢查處理著手，並與 issue 中連結的 Lua 7.3 參考資料進行比較。當該範例不再回報多餘回傳值警告時，即表示完成。

由索引模型根據 Issue 內容生成。