Improve error message when developing `teal` app

[donyunardi]

Summary

A descriptive error message is crucial for users when creating a teal app or module. Currently, stopifnot() is used for assertion in many of teal packages, without overriding the default message. As a result, users will encounter difficulty deciphering the message and may block development progress.

Definition of Done

• Replace stopifnot() with checkmate.
• User should receive a consistent and more user-friendly or actionable error message when developing teal app.

Triggered by:
insightsengineering/teal.transform/issues/99

[donyunardi]

Tasks

• Decide on better technique to replace stopifnot (checkmate?) I was informed that prior research has been done and checkmate is the appropriate solution.
• implement changes in teal's framework (teal, teal.data, teal.transform, teal.slice, teal.widget, teal.reporter)
  • We already implemented checkmate in most of the functions but I still see stopifnot in several functions.
• implement changes in teal's modules (tmg, tmc, to, tg)

Here's a screenshot of the number of lines of code that are still using stopifnot

Per discussion with @pawelru, we will approach this gradually by package instead of tackling them all at once.