Add converter from cql

There's probably quite a few **cql** (not **cql2**) examples out there in the wild, e.g. https://github.com/stac-utils/rustac-py/issues/135#issuecomment-2883481676 was taken from a **cql** example. It could be handy to provide a converter from **cql** to **cql2** as a part of this library. If there's a grammar for **cql**, maybe it wouldn't be too big a lift.

I envision the Rust crate just providing the conversion methods, and any downstream Python clients (either this one, **rustac**, or whatever) could link together the conversions in to nice "fallback" behaviors as they see fit.