Add --one-based option to dexplode-partition and dencode-partition

[jeromekelleher]

Useful for things that want to count from 1 to N inclusive.

Not sure what the nicest short form is, could do

vcf2zarr dexplode-partition -1 [ICF] [partition id]

but maybe that's confusing?

See #147

[benjeffery]

I think only having a long-form option of something like --1-based would be clearest.

[jeromekelleher]

Yeah, it's a fair starting point, can always add a short-form later if needed. I think best to fully spell though, like --one-based