feat: compile time completion generation

Removed `completion` command in favor of compile time completion
generation. This tool will only be build from source for the foreseeable
future so this makes sense for now.

build.rs

@@ -0,0 +1,22 @@
+use clap::{CommandFactory, ValueEnum};
+use clap_complete::{generate_to, Shell};
+use std::{env, io::Error};
+
+include!("src/cli/mod.rs");
+
+fn main() -> Result<(), Error> {
+    let outdir = match env::var_os("OUT_DIR") {
+        None => return Ok(()),
+        Some(outdir) => outdir,
+    };
+
+    let mut cmd = ahab::Ahab::command();
+
+    for shell in Shell::value_variants() {
+        let path = generate_to(*shell, &mut cmd, "ahab", &outdir)?;
+
+        println!("cargo:warning=completion file is generated: {path:?}");
+    }
+
+    Ok(())
+}