The type of keys used to index [] tables is not checked

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### 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

Some warning should be raised if you use [5] on a table, for example.

### Actual Behaviour

In the expression `tbl[x]`, the type of x is not checked at all

### Reproduction steps

```lua
---@type table -- or string[]
local IntStr = {}
---@type table
local StrInt = {}
IntStr[5] = "hi" -- ok
IntStr["a"] = "b" -- "a" should produce a warning
StrInt["a"] = 5 -- ok
StrInt[5] = 6 -- 5 should produce a warning
```

### Additional Notes

Probably related to #1861

### Log File

_No response_

Start with the Lua reproduction in the issue and inspect the type-checking path for table indexing. Verify that mismatched key types produce warnings for both integer-keyed and string-keyed tables, while the matching assignments remain valid.

Written by the indexing model from the issue text.