Move adjacent_difference to numeric header file

[dimitraka]

No description provided.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ -0.05%	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (8365e76)	201880	171929	85.16%
Head commit (29063b1)	190686 (-11194)	162309 (-9620)	85.12% (-0.05%)

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 (#6423)	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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[hkaiser]

@dimitraka could you please take care of the clang-format problems reported? The other issues are unrelated.