Correct std feature-flagging

If a crate has std set, it should enable std for all dependencies in order to
let them properly select which algorithms to use. Some crates fallback to
slower/worse algorithms on no-std.

Also more aggressively sets default-features = false leading to a *10%*
reduction in the amount of crates coordinator builds.

common/zalloc/Cargo.toml

@@ -17,5 +17,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 zeroize = { version = "^1.5", default-features = false }
 
 [features]
+std = ["zeroize/std"]
+default = ["std"]
 # Commented for now as it requires nightly and we don't use nightly
 # allocator = []