don't balance systems with rational coefficients

[baggepinnen]

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Difference	Reference Image	New Image
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✔️ 0.001
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❌ 0.046
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[codecov]

Codecov Report

Merging #670 (e1d73aa) into master (cd46c63) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #670   +/-   ##
=======================================
  Coverage   86.94%   86.94%           
=======================================
  Files          31       31           
  Lines        3308     3308           
=======================================
  Hits         2876     2876           
  Misses        432      432           

Impacted Files	Coverage Δ
src/types/conversion.jl	97.79% <100.00%> (ø)

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