Changes HashMap to use aHash instead, giving a performance boost. (#9391)

# Description

see https://github.com/nushell/nushell/issues/9390
using `ahash` instead of the default hasher. this will not affect
compile time as we where already building `ahash`.


# User-Facing Changes
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crates/nu-command/src/system/run_external.rs

@@ -1,4 +1,5 @@
 use crate::hook::eval_hook;
+use ahash::HashMap;
 use nu_engine::env_to_strings;
 use nu_engine::CallExt;
 use nu_protocol::{
@@ -11,7 +12,6 @@ use nu_protocol::{
 use nu_system::ForegroundProcess;
 use os_pipe::PipeReader;
 use pathdiff::diff_paths;
-use std::collections::HashMap;
 use std::io::{BufRead, BufReader, Read, Write};
 use std::path::{Path, PathBuf};
 use std::process::{Command as CommandSys, Stdio};