[Feat] Add setup completion tracking to prevent multiple setup calls

[JongtaekChoi]

PR Title

�� Type of change:

• ✨Feature/chore
• ♻️ Refactor
• 🔧 Bugfixes

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✏️ Description:

This PR added setup completion tracking to prevent multiple calls to the LINE SDK setup function. Fixes #186

Problem: The LINE SDK setup function could be called multiple times, causing app crashes or unexpected behavior due to internal SDK errors that developers couldn't properly handle.

Solution: Modified the setup method to check the existing LoginManager.shared.isSetupFinished property and reject with a clear error message when setup is already completed. This allows developers to handle the situation properly in the JavaScript layer instead of experiencing app crashes.

Key Changes:

• Added early return with reject("SETUP_ALREADY_COMPLETED", "Setup has already been completed", nil) when setup is already finished

Acceptance criteria:

• Setup method rejects with clear error when already completed
• JavaScript layer can properly handle the error
• App crashes prevented when setup is called multiple times
• Existing functionality remains unchanged for first-time setup calls

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🎥 Screen record:

N/A - This is a backend fix that doesn't require UI changes.

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📌 Notes:

• This change only affects the iOS implementation
• Uses existing LINE SDK property isSetupFinished instead of adding new variables
• No environment variables or configuration changes required
• Breaking change: Apps that don't handle the new error will need to add error handling

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✔️Tasks:

• Modify setup method to check LoginManager.shared.isSetupFinished
• Implement reject logic instead of resolve for already completed setup
• Ensure proper error handling in JavaScript layer
• Test setup flow to verify error handling works correctly

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⚠️ Warnings:

• Breaking Change: Apps that don't handle the SETUP_ALREADY_COMPLETED error will need to add try-catch blocks
• This fix is specific to iOS implementation only
• Android implementation may need similar changes if the same issue exists
• Relies on LINE SDK's internal setup tracking mechanism
• Developers should handle the error gracefully in their setup calls