Migrate tests for Splink 4 (ComparisonLevelCreator and ComparisonCreator and related changes)

[ADBond]

This is a branch to translate our existing (Splink 3) tests to work on the new ComparisonLevelCreator class (see #1689, #1703). This will be updated as and when new features get implemented in Splink 4, specifically the various missing comparison levels, and the library and template comparisons)

The changes to splink/ itself should all be relatively minimal, and mostly pertain to allowing the tests to run - anything sufficiently substantial will instead get its own PR to splink4_dev. That said, it is probably good to check the changes there particularly carefully in case I accidentally do anything silly.

The rest of the PR is large, but most of the changes should be fairly straightforward - mostly renaming + the small changes needed with updated syntax. I will try and highlight anything particularly noteworthy so that it doesn't get lost in the noise.

Progress:

Feature	Implemented	Added to this branch
Core levels (exact, null, else)	#1689	✅
LevenshteinLevel	#1689	✅
DatediffLevel	#1705 (+#1837)	✅
JaroWinklerLevel	#1717	✅
ColumnsReversedLevel	#1726	✅
JaroLevel	#1728	✅
JaccardLevel	#1728	✅
DamerauLevenshteinLevel	#1728	✅
DistanceInKMLevel	#1727	✅
ArrayIntersectLevel	#1753	✅
PercentageDifferenceLevel	#1758	✅
CustomLevel	#1768	✅
DistanceFunctionLevel	#1860	✅
or_	#1777	✅ (#1783)
and_	#1777	✅ (#1783)
not_	#1777	✅ (#1783)
ExactMatch	#1721	✅
LevenshteinAtThresholds	#1721	✅
CustomComparison	#1768	✅
DamerauLevenshteinAtThresholds	#1770	✅
JaccardAtThresholds	#1770	✅
JaroAtThresholds	#1770	✅
JaroWinklerAtThresholds	#1770	✅
DistanceInKMAtThresholds	#1815	✅ (#1816)
DatediffAtThresholds	#1782	✅
ArrayIntersectAtSizes	#1770	✅
DistanceFunctionAtThresholds	#1860	✅
EmailComparison	#1840	✅
DateComparison	#1856	✅ (#1857)
NameComparison	#1856	✅ (#1857)
PostcodeComparison	#1856	✅ (#1857)
ForenameSurnameComparison	#1856	✅ (#1857)
InputExpression (for regex_extract, lower, etc)	#1782	✅
comparison tf adjustments	#1812	✅ (#1813)
NullLevel regex validation	#1819 (+#1834)	✅
Paremeter validation (e.g. -ve array sizes)	#1861	✅

Tests now actually run [although some have been temporarily disabled], so we can start to get semi-useful feedback.

Number of failing tests [postgres, sqlite respectively in parentheses where included]:

110
96
93
85
64
55
52
57 😭
56
48
46
44
40
39
35
33 (5, 3)
33 (15, 12)
33 (5, 2)
31
32 😭
25 (5, 0)
24 (3, 0)
8 (4, 2)
8 (4, 0)
0 (0, 0) 🥳 🎉 🎊 ✅ 😎

[RobinL]

@ADBond to add datediff and the other levels I've done, shall i just do a PR pointing at this branch?

[ADBond]

@ADBond to add datediff and the other levels I've done, shall i just do a PR pointing at this branch?

It's okay, I have merged in splink4_dev + started changing all the relevant test modules

[RobinL]

thanks!

[RobinL]

Incredible work!