var_labels migrate to formatable

[wangh107]

close #151

[github-actions]

Code Coverage Summary

Filename                           Stmts    Miss  Cover    Missing
-------------------------------  -------  ------  -------  ---------
R/aet01.R                            142     142  0.00%    42-335
R/aet02.R                            163     163  0.00%    55-418
R/aet03.R                             61      61  0.00%    44-145
R/aet04.R                             67      67  0.00%    53-159
R/assertions.R                        23      23  0.00%    22-47
R/assertthat.R                         1       1  0.00%    3
R/cmt01a.R                           132     132  0.00%    52-376
R/cmt02_pt.R                          29      29  0.00%    36-92
R/dm_explicit_na.R                    44      44  0.00%    48-129
R/dmt01.R                             20      20  0.00%    48-113
R/dst01.R                            203     203  0.00%    5-542
R/egt01.R                             39      39  0.00%    45-122
R/ext01.R                             41      41  0.00%    40-176
R/gen_args.R                           1       1  0.00%    18
R/lbt01.R                             34      34  0.00%    43-111
R/mht01.R                             52      52  0.00%    41-125
R/sample_study_object.R               14      14  0.00%    14-35
R/standard_data_preprocessing.R      170     170  0.00%    38-456
R/utils.R                            130     130  0.00%    17-374
R/vst01.R                             40      40  0.00%    46-125
TOTAL                               1406    1406  0.00%

Results for commit: 66f0209c6566656decb3034291cc693c39ebc915

Minimum allowed coverage is 80%

♻️ This comment has been updated with latest results

[wangh107]

@BFalquet
Please help on fixing the R CMD check errors in the PR. Thanks!