Fix __all__ (#83)

The definition of `__all__` has never been correct, and it has not been
possible to import `*` from `pynvjitlink`, which resulted in an error
instead, e.g.:

```
In [1]: from pynvjitlink import *
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[1], line 1
----> 1 from pynvjitlink import *

File <frozen importlib._bootstrap>:1227, in _handle_fromlist(module, fromlist, import_, recursive)

File <frozen importlib._bootstrap>:1223, in _handle_fromlist(module, fromlist, import_, recursive)

TypeError: Item in pynvjitlink.__all__ must be str, not type
```

This fixes the issue by putting strings in `__all__`.

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pynvjitlink/__init__.py

@@ -3,4 +3,4 @@
 from pynvjitlink.api import NvJitLinker, NvJitLinkError
 from pynvjitlink._version import __version__
 
-__all__ = [NvJitLinker, NvJitLinkError, __version__]
+__all__ = ["NvJitLinker", "NvJitLinkError", "__version__"]