add license headers to python files

[pjfanning]

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• I had searched in the issues and found no similar issues.

Version

n/a

Component(s)

Python

Minimal reproduce step

n/a

What did you expect to see?

Apache RAT shows that these files don't header have license headers

  ./python/pyfury/__init__.pxd
  ./python/pyfury/_serialization.pyx
  ./python/pyfury/_util.pxd
  ./python/pyfury/_util.pyx
  ./python/pyfury/format/_format.pyx
  ./python/pyfury/format/encoder.pxi
  ./python/pyfury/format/row.pxi
  ./python/pyfury/format/vectorized.pxi
  ./python/pyfury/includes/__init__.pxd
  ./python/pyfury/includes/libabsl.pxd
  ./python/pyfury/includes/libformat.pxd
  ./python/pyfury/includes/libutil.pxd
  ./python/pyfury/lib/__init__.pxd
  ./python/pyfury/lib/mmh3/__init__.pxd
  ./python/pyfury/lib/mmh3/mmh3.pxd
  ./python/pyfury/lib/mmh3/mmh3.pyx

What did you see instead?

n/a

Anything Else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!