[Enhancement] Improve fun type matching

Nobody has claimed this yet.

```lua
---@class Class
---@field f fun(s: string): integer

---@param f fun(x: string): integer
local function handle(f)
return f("string")
end

-----

---@param i number
---@return boolean
local function is_positive(i)
return i >= 0
end

handle(is_positive) -- expect `param-type-mismatch`

---@type Class
local _ = { f = is_positive } -- expect `assign-type-mismatch`
```

Expected warning:
Type `fun(i: number):boolean` cannot match `fun(x: string):integer`

I didn't find duplicates, although I expected them
maybe I didn't search well

Start by reproducing the Lua snippet in the issue and tracing the function-type matching path used for the call and assignment checks. Done means both mismatches produce the expected `param-type-mismatch` and `assign-type-mismatch` warnings, including the reported function types.

Written by the indexing model from the issue text.