add support for generators to rs.concat

[kmdalton]

rs.concat does not support generators whereas pd.concat does. The reason rs does not support them, is that the control flow that checks whether the arguments are isomorphous specifically indexes the first element in the passed sequence. This only works for subscriptable objects. Instead, implementing this control flow using itertools.tee allows us to bypass the requirement that the passed sequence be subscriptable.

[codecov-commenter]

Codecov Report

Merging #74 (d4c29ec) into main (bcda297) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #74   +/-   ##
=======================================
  Coverage   98.91%   98.91%           
=======================================
  Files          39       39           
  Lines        1475     1477    +2     
=======================================
+ Hits         1459     1461    +2     
  Misses         16       16           

Flag	Coverage Δ
unittests	98.91% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
reciprocalspaceship/concat.py	100.00% <100.00%> (ø)

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[JBGreisman]

Looks good to me