Make Limbo core `no_std`

Discussed in https://github.com/tursodatabase/limbo/discussions/441

Originally posted by michalfita December 11, 2024 One of key features of original SQLite is that in can be built for bare metal system and used without OS in place on microcontrollers. To achieve the same, the core of Limbo would have to be no_std with ability to plug in a storage backend that's non-Linux thing. But I don't see #![no_std] clause in core's lib.rs.

Is this no-feature for Limbo being oriented for cloud solutions?