[Sample App] State saving with SavedStateHandle

[KeithYokoma]

It seems we are trying to restore the state from SavedStateHandle but not saving the state 😢 , so this PR fixes to save the state with SavedStateHandle properly.

[codecov-commenter]

Codecov Report

Merging #45 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #45   +/-   ##
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  Coverage   56.16%   56.16%           
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  Files           1        1           
  Lines          73       73           
  Branches       27       27           
=======================================
  Hits           41       41           
  Misses         23       23           
  Partials        9        9           

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