1109 athena datediff

[RossKen]

Type of PR

• BUG
• FEAT
• MAINT
• DOC

Is your Pull Request linked to an existing Issue or Pull Request?

Closes #1300
Closes #1109

Give a brief description for the solution you have provided

Datediff is useful across linkers, athena has a native function for it, so we should include in our cll libraries

PR Checklist

• Added documentation for changes
• Added feature to example notebooks at tutorials in splink_demos (if appropriate)
• Added tests (if appropriate)
• Made changes based off the latest version of Splink
• Run the linter

[github-actions]

Test: test_2_rounds_1k_duckdb

Percentage change: -32.9%

	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
1749	2023-06-20	15:00:57	1.26525	1.2588	(detached head)	102faf7	Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz	2.5939 GHz	102faf7

Test: test_2_rounds_1k_sqlite

Percentage change: -19.4%

	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
1751	2023-06-20	15:00:57	3.43709	3.43356	(detached head)	102faf7	Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz	2.5939 GHz	102faf7

Click here for vega lite time series charts

[ThomasHepworth]

I take it that the user entering an unexpected date_metric (unexpected for us here being anything other than day, month or year), then it will still calculate that without any issues?

[RossKen]

Yea, if it is valid in presto it should accept it fine

[ThomasHepworth]

I'm happy to approve this, even with the outstanding question.