Bug fixes and improving results for mixed models

[larmarange]

fix #238

• add unit tests

[codecov]

Codecov Report

Merging #239 (4c7e745) into main (637a9b0) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 4c7e745 differs from pull request most recent head 99294ff. Consider uploading reports for the commit 99294ff to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #239   +/-   ##
=======================================
  Coverage   95.48%   95.48%           
=======================================
  Files          43       43           
  Lines        2679     2679           
=======================================
  Hits         2558     2558           
  Misses        121      121           

Files	Coverage Δ
R/tidy_disambiguate_terms.R	100.00% <100.00%> (ø)
R/tidy_identify_variables.R	100.00% <100.00%> (ø)