Caching behavior in ConcatenateJob

[vieting]

The ConcatenateJob has currently hard-coded caching behavior.

gs.file_caching(str(i)) for i in self.text_files

In a case where I wanted to concatenate feature cache bundle files, this is suboptimal because caching the bundle (I think it's determined via the ending ".bundle") means caching all files inside that. That (a) takes unnecessarily long because we don't need to cache the content files and (b) - more importantly - is also wrong because the concatenated output file will contain the cached paths starting with /var/tmp/.

I used Path objects and set cached=False. The proposed change results in the intended behavior. Should we keep the compatibility for string inputs?

Also, I refactored the init function a bit.

[Atticus1806]

In general I would consider dropping string inputs generally. But since this would break potentially a lot, I would prefer to keep it in. But I really like the approach of not having it as a type.

[vieting]

In general I would consider dropping string inputs generally. But since this would break potentially a lot, I would prefer to keep it in. But I really like the approach of not having it as a type.

I also thought about this but was afraid that it breaks things, too. So I decided not to tackle that issue here.