process: make non-existent paths non-fatal, sort scan paths

[tstromberg]

scan --processes was exiting for me because qemu had been upgraded from under it. Now it logs an error, and also sorts the process list so that the scan results aren't jumping around so much.

Example run:

2024/10/06 22:34:07 ERROR qemu-system-aarch64[43299]: no such file or directory
🔎 Scanning "/Applications/Elastic Security.app/Contents/MacOS/Elastic Security"
🔎 Scanning "/Applications/Firefox Developer Edition.app/Contents/MacOS/firefox"
🔎 Scanning "/Applications/Firefox Developer Edition.app/Contents/MacOS/plugin-container.app/Contents/MacOS/plugin-container"
🔎 Scanning "/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/Versions/129.0.6668.71/Helpers/Google Chrome Helper (GPU).app/Contents/MacOS/Google Chrome Helper (GPU)"
🔎 Scanning "/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/Versions/129.0.6668.71/Helpers/Google Chrome Helper (Plugin).app/Contents/MacOS/Google Chrome Helper (Plugin)"
🔎 Scanning "/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/Versions/129.0.6668.71/Helpers/Google Chrome Helper (Renderer).app/Contents/MacOS/Google Chrome Helper (Renderer)"
🔎 Scanning "/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/Versions/129.0.6668.71/Helpers/Google Chrome Helper.app/Contents/MacOS/Google Chrome Helper"