feature request: attach a `reason` parameter to `@nodiscard`

Nobody has claimed this yet.

> [!NOTE]
> I couldn't find an issue for this. sorry if there's a duplicate.

I propose updating the `@nodiscard` annotation to add a "reason" as to why not discard the value:
```lua
---@nodiscard []
```
this would mirror Rust's `#[must_use = "reason"]` annotation.

### example:

```lua
---Creates a new class that inherits from this one.
---@return Class
---@nodiscard This method returns the new class; it's pointless to immediately discard it.
function Object:extend()
-- ...
end
```

discarding the output would then display the warning:
```md
* [warning][Lua Diagnostics.][discard-returns]
The return values of this function cannot be discarded:
This method returns the new class; it's pointless to immediately discard it.
```
note the colon at the end of "discarded".
if not given a reason, it would fall-back to the usual message, with "discarded" ending with a dot and no further explanation
(yes, I'm aware that reason in the Object:extend example isn't exactly... professional 😅)

No file or test is named. Start by locating the @nodiscard annotation parser and the discard-returns diagnostic, then trace how annotation text reaches that warning. Done means a supplied reason is displayed with the requested colon punctuation, while an omitted reason preserves the existing message and period.

Written by the indexing model from the issue text.