Accept human-readable sizes for keyspace --max-storage and --storage

[inelpandzic]

pscale keyspace update-settings --max-storage and --storage now accept sizes with a unit, such as 200GiB or 1.5TiB, in addition to a plain byte count.

pscale keyspace update-settings commerce main commerce --org myorg  --disk-scaling-strategy grow--max-storage 1TiB
pscale keyspace update-settings commerce main commerce --org myorg --disk-scaling-strategy shrink --storage 200GiB

Plain integers are still parsed exactly, so existing scripts that pass bytes are unaffected. Values that are zero or negative, not a valid size, or too large to fit in an int64 are rejected before any API call, and --storage must still be a multiple of 1 GiB. The --max-storage help text also documents the server-side limits.

Fixes https://github.com/planetscale/issues/issues/2020