Fix Duration parsing

[aminalaee]

Fixes #34

[lig]

@samuelcolvin this blocks #34 which we want for Pydantic V2 Beta 3 pydantic/pydantic#6096

[samuelcolvin]

otherwise idea looks good i think.

[codecov-commenter]

Codecov Report

Merging #35 (6dbfe4a) into main (aa33bd2) will increase coverage by 0.01%.
The diff coverage is 100.00%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   99.50%   99.51%   +0.01%     
==========================================
  Files           6        6              
  Lines         801      819      +18     
==========================================
+ Hits          797      815      +18     
  Misses          4        4              

Impacted Files	Coverage Δ
src/datetime.rs	96.62% <ø> (ø)
src/duration.rs	100.00% <100.00%> (ø)
src/time.rs	100.00% <100.00%> (ø)

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[samuelcolvin]

thanks so much.