Use snake case for file name

[SimonLab]

• Use snake_case for file name
• Remove unused import

[codecov[bot]]

Codecov Report

Merging #76 (8034c71) into main (9f684aa) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##              main       #76   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines           70        70           
=========================================
  Hits            70        70           

Impacted Files	Coverage Δ
demo_app/lib/main.dart	100.00% <ø> (ø)
demo_app/lib/repository/todo_repository.dart	100.00% <ø> (ø)
demo_app/lib/services/todo_service.dart	100.00% <ø> (ø)

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