[python-package] remove unnecessary allocations in ctypes code

[jameslamb]

A few places in the Python package use a pattern like the following:

ctypes.c_char_p(*[ctypes.addressof(string_buffer)])

That's identical to the following ...

ctypes.c_char_p(ctypes.addressof(string_buffer))

... except that it involves allocating, unpacking, and then immediately freeing a list object.

This PR proposes removing those unnecessary allocations, to make those code paths slightly faster and reduce their memory usage a tiny bit.

Notes for reviewers

Docs on ctypes.c_char_p() accepting a memory address as an int: https://docs.python.org/3/library/ctypes.html#ctypes.c_char_p

[github-actions]

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