[MAINT] Backend agnostic comparison composition tests

[ThomasHepworth]

Some quick tweaks to the comparison composition tests to make them backend agnostic.

[github-actions]

Test: test_2_rounds_1k_duckdb

Percentage change: -34.1%

	date	time	stats_mean	stats_min	commit_info_branch	commit_info_id	machine_info_cpu_brand_raw	machine_info_cpu_hz_actual_friendly	commit_hash
849	2022-07-12	18:40:05	1.89098	1.87463	splink3	c334bb9	Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz	2.7934 GHz	c334bb9
1758	2023-06-22	10:55:15	1.24531	1.23457	(detached head)	32eb67a	Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz	2.5939 GHz	32eb67a

Test: test_2_rounds_1k_sqlite

Percentage change: -19.8%

	date	time	stats_mean	stats_min	commit_info_branch	commit_info_id	machine_info_cpu_brand_raw	machine_info_cpu_hz_actual_friendly	commit_hash
851	2022-07-12	18:40:05	4.32179	4.25898	splink3	c334bb9	Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz	2.7934 GHz	c334bb9
1760	2023-06-22	10:55:15	3.41386	3.41381	(detached head)	32eb67a	Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz	2.5939 GHz	32eb67a

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[ThomasHepworth]

For testing, you just need to run:
python3 -m pytest -m all tests/test_comparison_level_composition.py -v

[ADBond]

Nice one, looks good - just a couple of comments but happy for you to address as you see fit + merge