chore: fix defaults for scale factors

[jo-mueller]

@will-moore very small fix that I discovered while working on #515 . In one of the entrypoints (write_labels), the Scaler class was still used as a default, which it shouldn't be.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.89%. Comparing base (cade24e) to head (52fb46a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #567      +/-   ##
==========================================
- Coverage   86.05%   85.89%   -0.17%     
==========================================
  Files          14       14              
  Lines        1857     1857              
==========================================
- Hits         1598     1595       -3     
- Misses        259      262       +3     

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