fix: Stop trimming trailing zeros when displaying decimals in SLT tests

[AdamGS]

Which issue does this PR close?

• Closes Decimal values in SLT tests lose display precision if they have trailing zeros #23835.

Rationale for this change

This change makes decimal display in SLT tests more explicit, making it easier to detect changes in precision/scale if the type is not asserted explicitly.

What changes are included in this PR?

Skip "normalizing" (which is just trimming trailing 0s) decimals on display in SLT tests.

Are these changes tested?

Existing tests, including changes to them, and one small SLT test.

Are there any user-facing changes?

None, this is test only.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.75%. Comparing base (1c8295c) to head (0eb0669).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23836      +/-   ##
==========================================
- Coverage   80.75%   80.75%   -0.01%     
==========================================
  Files        1089     1089              
  Lines      368809   368823      +14     
  Branches   368809   368823      +14     
==========================================
+ Hits       297837   297841       +4     
- Misses      53217    53225       +8     
- Partials    17755    17757       +2     

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[neilconway]

@AdamGS Can you take a look at the CI failures?

[AdamGS]

Ok figured out the issue - PG doesn't report scale, so we infer it from the number of digits in the fractional part.
this means that it doesn't pad out the zeros the same way this change does for data that comes from arrow/DF. I'll try and find a way to bridge this gap while keeping the data more exact.

[AdamGS]

I'm turning this PR into a draft while I try and find a solution here.