refactor/benchmarks: remove duplicate code and improve benchmark tests

[Fraser999]

This moves the generation of random data for benchmark tests outside of the actual code block being measured. It also removes code which was duplicated across all benchmark tests, and removes a needless benchmark test entirely.

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This change is

[dirvine]

Reviewed 1 of 1 files at r1. Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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_Comments from Reviewable_

[dirvine]

Reviewed 1 of 1 files at r2. Review status: all files reviewed at latest revision, all discussions resolved.

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_Comments from Reviewable_