Typo in 'ffi/primitives.dart'

This line reads:

https://github.com/dart-lang/samples/blob/main/ffi/primitives/primitives.dart#L46C1-L46C81

```
Directory.current.path, 'primitives_library', 'Debug', 'primtives.dll');
```

That `'primtives.dll'` should be `'primitives.dll'`, it's missing the second `i`

Open ffi/primitives/primitives.dart at line 46 and inspect the DLL path referenced in the issue. Correct the misspelled filename, then verify the sample now refers to primitives.dll and check the surrounding sample for any related spelling mismatch.

Written by the indexing model from the issue text.