Rename crate to veil-rs and update Nix scripts

Change package name from veil_rs to veil-rs.
Update Cargo.toml and Cargo.lock accordingly.
Update cargoHash in default.nix for the renamed package.
Comment out postInstall step that renamed the binary.
Rename `args` variable to `_args` in main.rs to silence unused warning.

src/main.rs

@@ -2,7 +2,7 @@ use std::io::Result;
 use veil_rs::cli::Cli;
 
 fn main() -> Result<()> {
-    let args: Cli = Cli::get_args();
+    let _args: Cli = Cli::get_args();
 
     Ok(())
 }