Factor out eps in pt transform

[veni-vidi-vici-dormivi]

Factor out the eps for readability.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 81.99%. Comparing base (9b0b76b) to head (94c5cb7).
Report is 29 commits behind head on main.

Files	Patch %	Lines
mesmer/mesmer_m/power_transformer.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #439      +/-   ##
==========================================
- Coverage   87.90%   81.99%   -5.92%     
==========================================
  Files          40       44       +4     
  Lines        1745     1938     +193     
==========================================
+ Hits         1534     1589      +55     
- Misses        211      349     +138     

Flag	Coverage Δ
unittests	81.99% <0.00%> (-5.92%)	⬇️

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