Using LuaJIT's nil-coalescing extension does not narrow the type correctly

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

Other

### Which OS are you using?

Linux

### What is the issue affecting?

Type Checking

### Expected Behaviour

Using the nil-coalescing operator should narrow an expressions type. For example, in this sample code, the type of `b` should be narrowed to `integer`:
```lua
---@type integer?
local foo = 1
local bar = foo ?? 2
```

### Actual Behaviour

Instead of the type being narrowed, the type of `foo` is copied instead, and the type of `bar` is thought to be `integer?` instead of `integer`.

### Reproduction steps

1. Insert the following sample code in a project:
```lua
---@type integer?
local foo = 1
local bar = foo ?? 2
```
2. Check the type of `b`

### Additional Notes

This seems to work fine using the classic Lua approach with `or`:
```lua
---@type integer?
local foo = 1
local bar = foo or 2
```
The type of `bar` is `integer` here, as expected.

### Log File

_No response_

Start by reproducing the issue in the lua-language-server type checker with the provided `??` example, then compare its inferred type with the equivalent `or` expression. Trace how the nil-coalescing expression handles nullable operands; done means `bar` is inferred as `integer` and the existing behavior remains correct for the comparison case.

Written by the indexing model from the issue text.