Add cli to Imports

[trangdata]

From June's comment:

Now that we have {rlang}, we're 1-step removed from also adding {cli} which I think may be worth considering later as QoL improvement: ex: warn() -> cli_warn(). The cli::cli_progress_*() functions can also replace our dependency to {progress}!

This is kind of a no brainer since cli is a tibble's dependency anyway.

[yjunechoe]

!! We can plan for a broad refactoring including:

• cat(), print()
• message(), warning(), stop()
• Miscellaneous signaling functions like .Deprecated(), packageStartupMessage(), etc.
• {rlang} warn() et al.
• {progress}