Fix a bug in the translation from 'human' frame ranges ('A-B,C-D') to
'Blender' frame ranges ('A..B,C..D'). It required calling
`string.replaceAll()` instead of `string.replace()` in the job compiler
script, which in turn required an upgrade of the JavaScript engine Goja.
Remove the `{ffmpeg}` variable from the default configuration, and its use
from the job compiler scripts. Now that the Worker can find its bundled
FFmpeg, it's no longer needed to configure its location on the Manager.
Refactor the JS script file loading code so that it's tied to the `fs.FS`
interface for longer, and less to the specifics of our `embed.FS` instance.
This should make it possible to use other filesystems, like a real on-disk
one, to load scripts.
