feat: methods for getting and refreshing long-lived tokens

[MikMik1011]

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I've implemented methods for getting and refreshing long-lived tokens for Threads users, allowing the app to stay authenticated without requiring reauthentication every hour.

Additionally, I refactored the authorization code exchange method to use the internal _apiPost method, ensuring consistency across the codebase.

I’ve manually tested these changes, and everything works as expected with no impact on other parts of the codebase.