zram unit implementation

[nekopsykose]

examples:

https://github.com/vaeth/zram-init
https://github.com/systemd/zram-generator

kernel:

https://www.kernel.org/doc/html/next/admin-guide/blockdev/zram.html

[nekopsykose]

system units aside, a cli example:

# modprobe zram num_devices=1 # /dev/zram{0,1, ...}
# zramctl --algorithm zstd --size 8G /dev/zram0
# mkswap /dev/zram0
# swapon /dev/zram0 # instead of swap, one can also mount this to /tmp for compressed tmpfs, etc