Fix dfuhelper slowness (mainly on macOS) (#351)

system_profiler takes ~0.2s on my MacBook Air M1 and it was being called
twice per second. I made it so it's only called once per second and also
put the whole check on a background thread to ensure the countdown
doesn't get slowed down.

palera1n.sh

@@ -41,10 +41,15 @@ remote_cp() {
 }
 
 step() {
+    rm -f .entered_dfu
     for i in $(seq "$1" -1 0); do
-        if [[ $(get_device_mode) == "dfu" || ($1 == "10" && $(get_device_mode) != "none") ]]; then
+        if [[ -e .entered_dfu ]]; then
+            rm -f .entered_dfu
             break
         fi
+        if [[ $(get_device_mode) == "dfu" || ($1 == "10" && $(get_device_mode) != "none") ]]; then
+            touch .entered_dfu
+        fi &
         printf '\r\e[K\e[1;36m%s (%d)' "$2" "$i"
         sleep 1
     done
@@ -200,7 +205,8 @@ _reset() {
 
 get_device_mode() {
     if [ "$os" = "Darwin" ]; then
-        apples="$(system_profiler SPUSBDataType 2> /dev/null | grep -B1 'Vendor ID: 0x05ac' | grep 'Product ID:' | cut -dx -f2 | cut -d' ' -f1 | tail -r)"
+        sp="$(system_profiler SPUSBDataType 2> /dev/null)"
+        apples="$(printf '%s' "$sp" | grep -B1 'Vendor ID: 0x05ac' | grep 'Product ID:' | cut -dx -f2 | cut -d' ' -f1 | tail -r)"
     elif [ "$os" = "Linux" ]; then
         apples="$(lsusb | cut -d' ' -f6 | grep '05ac:' | cut -d: -f2)"
     fi
@@ -244,7 +250,7 @@ get_device_mode() {
     if [ "$os" = "Linux" ]; then
         usbserials=$(cat /sys/bus/usb/devices/*/serial)
     elif [ "$os" = "Darwin" ]; then
-        usbserials=$(system_profiler SPUSBDataType 2> /dev/null | grep 'Serial Number' | cut -d: -f2- | sed 's/ //')
+        usbserials=$(printf '%s' "$sp" | grep 'Serial Number' | cut -d: -f2- | sed 's/ //')
     fi
     if grep -qE '(ramdisk tool|SSHRD_Script) (Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) [0-9]{1,2} [0-9]{4} [0-9]{2}:[0-9]{2}:[0-9]{2}' <<< "$usbserials"; then
         device_mode=ramdisk