CSUP: Allow multiple objects

[mattnibs]

This pr changes the protocol for CSUP files so that a single file can contain multiple vng Objects. When writing a CSUP file a new object is created every 120,000 values.

[mattnibs]

I should say there's an issue with this pr in the vcache.Cache expects a file to have a single object which in turn has a single vector. I'm not sure what to do about this but since we're not really worrying about lakes at this point I kind of think we should punt on this area for the time being.

[philrz]

Note to self: Per a heads up from @mattnibs, I'll need to recreate the CSUP files used for mgbench once this merges so we can take advantage of parallel reads.

[mccanne]

I should say there's an issue with this pr in the vcache.Cache expects a file to have a single object which in turn has a single vector. I'm not sure what to do about this but since we're not really worrying about lakes at this point I kind of think we should punt on this area for the time being.

We just need to name objects as ksuid:obj# and we can keep everything the same for now. Later we can add metadata that spans the objects in a file but that is stilled keyed on ksuid so I think it all hangs.

[mccanne]

cool!