Consider PATH when running command is nuscript in windows (#15486)

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Fixes #15476

# Description
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Consider PATH when checking for potential_nuscript_in_windows to allow
executing scripts which are in PATH without having to full path address
them. It previously only checked the current working directory so only
relative paths to cwd and full path worked.

The current implementation runs this then through cmd.exe /D /C which
can run it with assoc and ftype set for nushell scripts.
We could instead run it through nu as `std::env::current_exe()` avoiding
the cmd call and the need for assoc and ftype (see:
8b25173f02).
But ive left the current implementation for this intact to not change
implementation details, avoid a bigger change and leave this open for
discussion here since im not sure if this has any major implications.

# User-Facing Changes
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This would now run every external command through PATH an additional
time on windows, so potentially twice. I dont think this has any bigger
effect.

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crates/nu-command/src/system/run_external.rs

@@ -78,6 +78,8 @@ impl Command for External {
             _ => Path::new(&*name_str).to_owned(),
         };
 
+        let paths = nu_engine::env::path_str(engine_state, stack, call.head)?;
+
         // On Windows, the user could have run the cmd.exe built-in "assoc" command
         // Example: "assoc .nu=nuscript" and then run the cmd.exe built-in "ftype" command
         // Example: "ftype nuscript=C:\path\to\nu.exe '%1' %*" and then added the nushell
@@ -88,7 +90,7 @@ impl Command for External {
         // easy way to do this is to run cmd.exe with the script as an argument.
         let potential_nuscript_in_windows = if cfg!(windows) {
             // let's make sure it's a .nu script
-            if let Some(executable) = which(&expanded_name, "", cwd.as_ref()) {
+            if let Some(executable) = which(&expanded_name, &paths, cwd.as_ref()) {
                 let ext = executable
                     .extension()
                     .unwrap_or_default()
@@ -133,7 +135,6 @@ impl Command for External {
         } else {
             // Determine the PATH to be used and then use `which` to find it - though this has no
             // effect if it's an absolute path already
-            let paths = nu_engine::env::path_str(engine_state, stack, call.head)?;
             let Some(executable) = which(&expanded_name, &paths, cwd.as_ref()) else {
                 return Err(command_not_found(
                     &name_str,