Support half open ranges

[arpad-m]

Both the standard Range HTTP header (or range in HTTP/2 lingo) as well as the x-ms-range header support half open ranges, meaning ones like bytes=1234-.

https://learn.microsoft.com/en-us/rest/api/storageservices/specifying-the-range-header-for-blob-service-operations

The SDK's Range type does not however: it always requires an end to be specified.

As the end is exposed, it would be a semver breaking change to turn the end field on the Range into an option (or even a bool field has_end or such as the struct is exhaustively public).

[demoray]

If this is something we include, we might do something akin to the SliceIndex trait, where it supports multiple of the base range types (including RangeFrom).

[arpad-m]

The spec for the range header says that there is two possible ranges, one "int range" which has an obligatory start and an optional end, and one "suffix range", which has no start but an end. Then the range header is a comma seperated list of int or suffix ranges.