improvement: improve cli startup performance using v8 cache (#6049)

* feat: experimental flag to enable v8 cache

This can speed up the core command startup time.

Can be enabled by now using `GARDEN_COMPILE_CACHE=1` and is disabled by
default.

On my M2 mac it saves ~11-30ms when running `garden --help`

* improvement: enable v8 cache by default

garden-sea/src/node.rs

@@ -39,6 +39,18 @@ where
     #[cfg(all(target_os = "linux"))]
     command.env("GARDEN_SEA_TARGET_ENV", TARGET_ENV);
 
+    // Enable v8 compilation cache by default. That saves ~10-30ms on an M2 mac and we've seen 2 seconds startup time shaved off on Windows.
+    // See also https://nodejs.org/api/cli.html#node_compile_cachedir
+    let enable_compile_cache = env::var("GARDEN_COMPILE_CACHE").unwrap_or("true".into());
+    if enable_compile_cache == "true" || enable_compile_cache == "1" {
+        let cache_dir = path.join("v8cache");
+        fs::create_dir_all(cache_dir.clone())?;
+        command.env(
+            "NODE_COMPILE_CACHE",
+            OsString::from(cache_dir),
+        );
+    }
+
     // Allow users to override the heap size if needed.
     let max_old_space_size = env::var("GARDEN_MAX_OLD_SPACE_SIZE").unwrap_or("4096".into());
     let max_semi_space_size = env::var("GARDEN_MAX_SEMI_SPACE_SIZE").unwrap_or("64".into());