fix: file copyright headers

[jkowalleck]

utilizes flake8 plugin https://pypi.org/project/flake8-copyright-validator/ to assert the correct headers

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00%	✅ ∅ (target: 80.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (934d39d)	4512	4193	92.93%
Head commit (5974a8f)	4512 (+0)	4193 (+0)	92.93% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#676)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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