`unknown-cast-variable` in last function of a file

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?

Windows

### What is the issue affecting?

Type Checking

### Expected Behaviour

I have a file with two functions that both cast a local variable to a different type. This works perfectly for the first function but fails for the second (or the last if I add more functions).

### Actual Behaviour

Error `Unknown type conversion variable item (unknown-cast-variable)` for the `---@cast item B` inside `fu()`.

### Reproduction steps

```lua
---@alias A table
---@alias B table

---@type table
local items = {}

function fu()
local item = items[1]
---@cast item B
end

function bar()
local item = items[1]
-- Error appears here:
---@cast item B
end
```

### Additional Notes

_No response_

### Log File

_No response_

從 issue 中的 Lua 重現開始，追蹤 language server 如何處理跨連續函式的 `---@cast` 變數。比較 `fu()` 中成功的 cast 與 `bar()` 中失敗的 cast；當兩個 cast 都能在沒有 `unknown-cast-variable` 的情況下被接受時，即表示完成。

由索引模型根據 Issue 內容生成。