feat: Wrap sodium_malloc as a custom allocator

This lets us get rid of quite a few unsafe blocks.

Cargo.toml

@@ -42,6 +42,7 @@ paste = "1.0.12"
 env_logger = "0.10.0"
 toml = "0.7.4"
 static_assertions = "1.1.0"
+allocator-api2 = "0.2.16"
 log = { version = "0.4.17" }
 clap = { version = "4.3.0", features = ["derive"] }
 serde = { version = "1.0.163", features = ["derive"] }