IMO it would be good to familiarize yourself with the rust quirks/features (check out the rust book) and then poke at some of the embedded specific groups. Once you get a handle on the common types and patterns it's probably easier to find the information you're looking for, e.g.:
In general Rust chases a "zero cost abstraction" ethos, so a lot of the type system niceties have no code or memory cost because the heavy lifting is done at compile time, not run time. For instance using specific traits for each GPIO pin ensures you won't accidentally apply some meaning meant for another pin, but the compiler will compile it right down to integers anyhow.
Things like options (how Rust deals with "null" values) are enums and usually incur a one byte penalty, but in some cases they can be compiled down to no overhead at all.
https://github.com/rust-lang/rust/issues/46213
In general Rust chases a "zero cost abstraction" ethos, so a lot of the type system niceties have no code or memory cost because the heavy lifting is done at compile time, not run time. For instance using specific traits for each GPIO pin ensures you won't accidentally apply some meaning meant for another pin, but the compiler will compile it right down to integers anyhow.
Things like options (how Rust deals with "null" values) are enums and usually incur a one byte penalty, but in some cases they can be compiled down to no overhead at all.