grimblast: support cursor in frozen area capture

[shovel-kun]

Description of changes

Allow grimblast --freeze --cursor ... area now that hyprpicker can include the cursor in its frozen screencopy.

Fixes #92 (with the caveat that it only works with hardware cursors, software cursors still borked).
Depends on hyprwm/hyprpicker#156.

• For new programs

  • Add the program to the README table, with yourself as the maintainer
  • Add a README for the program itself
  • Add Makefile (and Nix derivation optionally, otherwise @fufexan will do it)
  • If the program is a script, add it to the CI checks matrix

• For changes

  • Add changes to the CHANGELOG
  • Reflect your changes in the man pages (if they exist)

Example: (notice there's no double cursor)

[fufexan]

Why have CURSOR and CAPTURE_CURSOR? Can't we use one variable?

Also, how will this work with existing hyprpicker versions?