chore: Prep for CRAN release

fix: Placeholder type updates

* The following "placeholder" pattern updates (#83):

  + The following placeholder pattern names are now serviced by lucidinternets.com:

    - "cage" and "cagebw"
    - "murray" and "murraybw"
    - "seagal" and "seagalbw"

  + The following placeholder pattern names have been removed since their associated web service no longer works:

    - "lorempixel" and "lorempixelbw" (service unavailable since 2022)
    - "placeimg" and "placeimgbw" ([support officially ended July 2023](https://www.gomasuga.com/placeimg?souce=placeimg))

  + The "dummybw" name now provides a pure black-and-white image (i.e. no grey).
  + Fixes a regression for the "placeholderbw" name where it redirected to the "segal" name instead of "placeholder".

closes #83

chore: Prep for CRAN release

fix: Skip "text" pattern example in `pdf()`

* "text" pattern example now skipped if ran within certain graphics devices like `pdf()`
  that can't handle the playing cards Unicode glyphs (#68).

closes #68

feat: 'reset_image_cache()'

* `reset_image_cache()` resets the image cache used by `grid.pattern_image()`
   and `grid.pattern_placeholder()` to store images (#63).

closes #25, closes #63

chore: Bump Github Actions check to 'v2'

* 'v1' is deprecated so we bump to 'v2'

chore: Put some examples in \donttest{}

* CRAN release was rejected because on one of the pre-check machines
  a couple of examples took more than 10 seconds
* We wrap those examples in a \donttest{}

chore: Prep for CRAN patch release

chore: Bump versions for CRAN release

chore: Update CRAN comments [skip ci]