Fix difftime bug for CRAN

[adamkucharski]

A new change in r-devel affects how unique() behaves. Previously, calling unique() on a difftime object returned a numeric vector, but now it retains its difftime class.

Hence the following check in cfr_static, cfr_rolling and cfr_time_varying now fails:

identical(unique(diff(data$date)), 1)

because diff(data$date) returns a difftime object, and unique(diff(data$date)) no longer simplifies to numeric.

It has therefore been replaced with:

identical(unique(as.numeric(diff(data$date))), 1)

Once this PR is complete, we'll release version 0.13 onto CRAN with the above fix.

[Bisaloo]

I can confirm the example issues are gone on R devel:

R.version
#>                _                                                 
#> platform       x86_64-pc-linux-gnu                               
#> arch           x86_64                                            
#> os             linux-gnu                                         
#> system         x86_64, linux-gnu                                 
#> status         Under development (unstable)                      
#> major          4                                                 
#> minor          5.0                                               
#> year           2025                                              
#> month          02                                                
#> day            02                                                
#> svn rev        87676                                             
#> language       R                                                 
#> version.string R Under development (unstable) (2025-02-02 r87676)
#> nickname       Unsuffered Consequences

^{Created on 2025-02-06 with reprex v2.1.1}