[#51] Revise exceptions handling

[YuriRomanowski]

Description

Problem: Currently we use ExceptT BotException IO which is inconvenient because both BotException, other sync exceptions and async exceptions should be handled separately.

Solution: Remove ExceptT, use UnliftIO for exceptions handling, also use UnliftIO for asyncs instead of monad-control.

Related issue(s)

Fixed #51

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