atproto utils for zig zat.dev

miscellaneous enhancements #32

Merged resonancel.tngl.sh
targeting main from resonancel.tngl.sh/zat:dev
Merged opened by and assigned to resonancel.tngl.sh
targeting main from resonancel.tngl.sh/zat:dev
Commits 7

added EphemeralCar for stream writing
fixed and enhanced Tid
minor touch-ups on multibase
removed unnecessary nesting in `Datetime.zig`
renamed `datetime.zig` into `Datetime.zig`
optimized datatime
converted Tid into packed struct