Like most modern languages, Rust has its own build system and package manager, Cargo. Everything you're referring to relates to that, and has nothing to do with LLM coding.
Edit: saw the clarification in another comment. But, in that case the essential point seems to be "I'm not familiar with something, therefore it's suspect."
The project itself seems to be structued around 1.4k micro-crates[0] which I admit is a bit weird. Rust's compilation unit is the crate unlike C's per-file compilation unit, so if this was a 1:1 AI-assisted translation from the original Postgres source this might be an artifact of the translation.
This is correct. We first used c2rust to translate the C into unsafe Rust. The generated Rust code had one crate per C compilation unit. We then took the unsafe unidiomatic Rust and one crate at a time converted it to safe Rust.