Allow disabling inlining for MultiZarrToZarr

[maresb]

I am trying to combine some massive S3-based Zarr references. A MultiZarrToZarr operation which would otherwise take a minute would take days because the size of each file on S3 is being queried. Thus I want to be able to pass in inline_threshold=None so that my datasets combine in a reasonable timeframe.

[martindurant]

I think this was already possible with inline_threashold=0 ?

[maresb]

Nope, if inline_threshold=0 then fs.info(fn) still gets called in order to ensure that the file size isn't negative. 😅

We could change this so that we use 0 in place of None. That would probably make more sense actually. Then my conditional self.inline is not None becomes self.inline > 0.

[martindurant]

That sounds like a good plan