* Eliminate the need for Stream magic strings & added additional XGROUP subcommands.

- Replaced the need for magic strings with Range, ReadOffset, and GroupReadOffset structs.
- Condensed some of the method signatures due to the new structs.
- Added methods & tests for two of the XGROUP subcommands (DESTROY & DELCONSUMER).

* Updated tests with their original IDs used.

* Use a single struct to represent stream position for Group, Read, and ReadGroup commands.

- Consolidated GroupCreateOptions, GroupReadOffset, and ReadOffset into a single struct, Position.
- Removed the "Pair" structs and created StreamPosition, this will be used in the multi-stream read commands.
- Renamed RedisStreamEntry to StreamEntry.
- Also added the remaining subcommand for the XGROUP command (SETID) and an associated unit test.

* File cleanup, delete consolidated structs.

* Additional changes and unit tests for the Position struct.

* Update PositionKind enum with explicit zero value.