feat: retranslate keys updated in main locale

[lukepighetti]

https://x.com/luke_pighetti/status/1803755924793811402

perhaps we could save the main locale arb from the last translation on disk, ideally colocated with the project (.dart_tool?), and then do a diff on values, and thus create a list of keys from the main locale that have changed

perhaps this could be configured with

arb-translate-changed-values: true # default false

arb_translate --changed-values=true # default false