Features from optional dependencies

alloc implicit feature

Enables rustc-std-workspace-alloc

rustc-std-workspace-alloc:

crate for integration of crates.io crates into rust-lang/rust standard library workspace

core implicit feature

Enables rustc-std-workspace-core

rustc-std-workspace-core:

crate for integration of crates.io crates into rust-lang/rust standard library workspace