feat: add cd builtin command

src/builtins/cd.rs

@@ -0,0 +1,8 @@
+use std::env::set_current_dir;
+
+use crate::error::ShellError;
+
+pub fn run(keyword: &str, args: &[&str]) -> Result<(), ShellError> {
+    set_current_dir(args[0]);
+    Ok(())
+}

src/builtins/mod.rs

@@ -1,11 +1,16 @@
 use crate::error::ShellError;
+mod cd;
 
-const BUILTINS: &[&str] = &[];
+const BUILTINS: &[&str] = &["cd"];
 
 pub fn is_builtin(keyword: &str) -> bool {
     BUILTINS.contains(&keyword)
 }
 
 pub fn execute_builtin(keyword: &str, args: &[&str]) -> Result<(), ShellError> {
+    match keyword {
+        "cd" => cd::run(keyword, args)?,
+        _ => {}
+    }
     Ok(())
 }