Add distance_threshold check

[ThomasHepworth]

Type of PR

• BUG
• FEAT
• MAINT
• DOC

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

#1717

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Adds a quick validation check to the distance_threshold value, erroring out should an invalid threshold be entered by the user.

Error demo

import splink.comparison_level_library as cll

# Passes
cll.JaroWinklerLevel("test", 0.8).get_comparison_level("duckdb")

# Errors
cll.JaroWinklerLevel("test", 1.2)

I'm happy to close this if you'd rather not add this in, or, would rather add it in at a later date.

Note - we may want to change the function to only check values between 0 and 1 (remove the upper and lower bound args), making the code easier to read, but reducing flexibility. However, given our current suite of distance functions, I believe this is fine (the lev function family really only wants to check that n > 0).

PR Checklist

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[RobinL]

Love it