Fix `_polyprep`, `PolynomialRatio`, for `Number` args

[wheeheee]

The current implementation uses reverse(x), which is a method error for Number arguments. Thus PolynomialRatio(::Number, ::Number) doesn't work as currently documented. ~This commit also reduces runtime dispatch.~ edit: guess it doesn't because of all the inlining anyway

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.40%. Comparing base (4ff6208) to head (a4cfd09). Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #571   +/-   ##
=======================================
  Coverage   97.40%   97.40%           
=======================================
  Files          16       16           
  Lines        3193     3193           
=======================================
  Hits         3110     3110           
  Misses         83       83           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.