`check_is_recent` gives wrong result for epiweeks

[brookslogan]

library(epidatr)
#> ! epidatr cache is being used (set env var EPIDATR_USE_CACHE=FALSE if not
#>   intended).
#> ℹ The cache directory is ~/.cache/R/epidatr.
#> ℹ The cache will be cleared after 14 days and will be pruned if it exceeds 4096
#>   MB.
#> ℹ The log of cache transactions is stored at ~/.cache/R/epidatr/logfile.txt.
library(magrittr)
today <- as.Date("2025-08-07")
analysis_as_of_date <- today - 14L
analysis_as_of_epiweek <- MMWRweek::MMWRweek(analysis_as_of_date) %>%
  {.$MMWRyear*100 + .$MMWRweek}
tbl <- pub_flusurv("network_all", "*", issues = epirange(123401, analysis_as_of_epiweek))
#> Warning: Using cached results with `as_of` within the past week (or the future!). This
#> will likely result in an invalid cache. Consider
#> ℹ disabling the cache for this session with `disable_cache` or permanently with
#>   environmental variable `EPIDATR_USE_CACHE=FALSE`
#> ℹ setting `EPIDATR_CACHE_MAX_AGE_DAYS=1` to e.g. `3/24` (3 hours).
#> This warning is displayed once every 8 hours.

^{Created on 2025-08-07 with reprex v2.1.1}

This can be traced back to check_is_recent comparing the epiweek number with the stringified date "20250731".