feat: implement GetUserByIdUseCase in Application layer / Application層のGetUserByIdUseCase実装

[zigzagdev]

Motivation / 目的

Implement the Application layer for the User findById API as part of #507.

#507 の一環として、ユーザー取得APIのApplication層を実装しました。

What I have done / 実施内容

• GetUserByIdUseCase: call UserRepositroyInterface::findById() and return UserDto
  • Throw Exception with message 'User not found.' when the user does not exist

Test Results / テスト結果

• test_handle_returns_user_dto_when_user_exists
• test_handle_throws_exception_when_user_not_found

Closes #508

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.78%. Comparing base (016762b) to head (ef5b062).

Additional details and impacted files

@@                    Coverage Diff                     @@
##             feat/user_find_by_id     #511      +/-   ##
==========================================================
+ Coverage                   58.57%   58.78%   +0.20%     
- Complexity                   1471     1478       +7     
==========================================================
  Files                         112      114       +2     
  Lines                        7467     7505      +38     
==========================================================
+ Hits                         4374     4412      +38     
  Misses                       3093     3093              

Files with missing lines	Coverage Δ
...yUseCases/Tests/UseCase/GetUserByIdUseCaseTest.php	100.00% <100.00%> (ø)
.../QueryUseCases/UseCase/User/GetUserByIdUseCase.php	100.00% <100.00%> (ø)

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[zigzagdev]

ok