🧹 refactor: remove repetitive parameter passing in IconAsyncButton

[esenmx]

🎯 What:
Refactored IconAsyncButton to eliminate repetitive parameter passing across IconButton constructor variants (standard, filled, filledTonal, outlined). Introduced a private _buildIconButton method using constructor tear-offs.

💡 Why:
Reduces boilerplate code and repetition in build(), improving maintainability and readability without altering behavior or API.

✅ Verification:
Passed flutter analyze and all package tests via flutter test.

✨ Result:
Cleaner and more maintainable IconAsyncButton implementation.

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PR created automatically by Jules for task 4206677125264470908 started by @esenmx

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