Improve error messages

[olivroy]

Also added favicons and upgraded to testthat 3rd edition.

This doesn't add any Imports to the package since dplyr imports cli already.

had to modify the lintr config due to r-lib/lintr#2252, r-lib/lintr#2416

[larmarange]

Thank you for your PR.

I will merge it next week before submitting a new release of labelled

[codecov]

Codecov Report

Attention: Patch coverage is 94.23077% with 3 lines in your changes missing coverage. Please review.

Project coverage is 93.45%. Comparing base (9d0533c) to head (3acff69).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
R/remove_labels.R	70.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   93.42%   93.45%   +0.03%     
==========================================
  Files          18       18              
  Lines        1308     1284      -24     
==========================================
- Hits         1222     1200      -22     
+ Misses         86       84       -2     

Files with missing lines	Coverage Δ
R/copy_labels.R	100.00% <100.00%> (ø)
R/na_values.R	94.33% <100.00%> (-0.11%)	⬇️
R/to_labelled.R	95.78% <100.00%> (+3.78%)	⬆️
R/val_labels.R	93.45% <100.00%> (-0.32%)	⬇️
R/var_label.R	99.04% <100.00%> (-0.06%)	⬇️
R/remove_labels.R	90.24% <70.00%> (-2.26%)	⬇️