Add safety dependency to alloc and std crates

Just as previously done for core: this will enable future use of
`safety::{ensures,requires}` in those crates.

library/alloc/Cargo.toml

@@ -11,6 +11,7 @@ edition = "2021"
 [dependencies]
 core = { path = "../core" }
 compiler_builtins = { version = "0.1.123", features = ['rustc-dep-of-std'] }
+safety = { path = "../contracts/safety" }
 
 [dev-dependencies]
 rand = { version = "0.8.5", default-features = false, features = ["alloc"] }

library/std/Cargo.toml

@@ -26,6 +26,7 @@ hashbrown = { version = "0.14", default-features = false, features = [
 std_detect = { path = "../stdarch/crates/std_detect", default-features = false, features = [
     'rustc-dep-of-std',
 ] }
+safety = { path = "../contracts/safety" }
 
 # Dependencies of the `backtrace` crate
 rustc-demangle = { version = "0.1.24", features = ['rustc-dep-of-std'] }