Macro build 

macro_rules! build {
    ($file:expr) => { ... };
}

Embed the shared Canic configuration into a canister crate’s build script.

Reads the provided TOML file (relative to the workspace root), validates it using Config, exposes relevant cfg flags, and sets CANIC_CONFIG_PATH for later use by include_str!. Canister crates typically invoke this from build.rs.