rustac: the power of Rust for the STAC ecosystem

[gadomski]

👋🏼 Hey folks! I've renamed my stac-rs package to rustac. For context and rationale, see stac-utils/rustac#641.

The biggest downstream effect is if you've been using the stacrs Python package — you need update to rustac: pip install rustac.

Hopefully we've done this change early enough in the adoption of rustac that it doesn't blow up too many people's workflows. h/t @m-mohr for the slogan "the power of Rust for the STAC ecosystem"