Restructure analysis results + add visit variable to pool data.frame

[pengguanya]

@gowerc @nociale
update based on 255-01

• convert all dplyr, rlang, purrr related functions to base
• use assert_that instead of stop_if_not
• add and update tests for utility，analysis and ancova functions
• make new analysis result class correctly handle NA values
• fix some bugs

Tests are passed for analyse, analysis_result, ancova and utilities, but there are still tests and functions (mainly pool relevant ones) need to be updated. I will look into that while updating pool next week

[pengguanya]

@gowerc @nociale
The pool function has been updated and it works now with the new analysis_result class. All tests in test-pool.R are passed. I do have a few questions though and will post in the the discussion together with relevant code.

[pengguanya]

@gowerc @nociale
Final update is done and full tests passed. Please review

[gowerc]

Hey @pengguanya ,

Apologies for leaving this so long. Just to say I got around to fixing the issue that was blocking the CICD tests. We also had to create an emergancy update for the package which I've merged into your branch here for you. That being said now that the unit tests are running I am seeing some failures on this PR:

The vignettes don't appear to be working:
https://github.com/insightsengineering/rbmi/actions/runs/3291480479/jobs/5425686328

Theres an issue with the document() function but I need to look into that myself.

Also looks like some of the snapshot tests have updated which I don't think I was expecting to happen:
https://github.com/insightsengineering/rbmi/actions/runs/3291480281/jobs/5425685856