Mitigate the poor interaction between ndots expansion and non-path strings (#13218)

# Description

@hustcer reported that slashes were disappearing from external args
since #13089:

```
$> ossutil ls oss://abc/b/c
Error: invalid cloud url: "oss:/abc/b/c", please make sure the url starts with: "oss://"

$> ossutil ls 'oss://abc/b/c'
Error: oss: service returned error: StatusCode=403, ErrorCode=UserDisable, ErrorMessage="UserDisable", RequestId=66791EDEFE87B73537120838, Ec=0003-00000801, Bucket=abc, Object=
```

I narrowed this down to the ndots handling, since that does path parsing
and path reconstruction in every case. I decided to change that so that
it only activates if the string contains at least `...`, since that
would be the minimum trigger for ndots, and also to not activate it if
the string contains `://`, since it's probably undesirable for a URL.

Kind of a hack, but I'm not really sure how else we decide whether
someone wants ndots or not.

# User-Facing Changes
- bare strings not containing ndots are not modified
- bare strings containing `://` are not modified

# Tests + Formatting
Added tests to prevent regression.

crates/nu-command/tests/commands/run_external.rs

@@ -229,6 +229,38 @@ fn external_command_escape_args() {
     })
 }
 
+#[test]
+fn external_command_ndots_args() {
+    let actual = nu!(r#"
+        nu --testbin cococo foo/. foo/.. foo/... foo/./bar foo/../bar foo/.../bar ./bar ../bar .../bar
+    "#);
+
+    assert_eq!(
+        actual.out,
+        if cfg!(windows) {
+            // Windows is a bit weird right now, where if ndots has to fix something it's going to
+            // change everything to backslashes too. Would be good to fix that
+            r"foo/. foo/.. foo\..\.. foo/./bar foo/../bar foo\..\..\bar ./bar ../bar ..\..\bar"
+        } else {
+            r"foo/. foo/.. foo/../.. foo/./bar foo/../bar foo/../../bar ./bar ../bar ../../bar"
+        }
+    );
+}
+
+#[test]
+fn external_command_url_args() {
+    // If ndots is not handled correctly, we can lose the double forward slashes that are needed
+    // here
+    let actual = nu!(r#"
+        nu --testbin cococo http://example.com http://example.com/.../foo //foo
+    "#);
+
+    assert_eq!(
+        actual.out,
+        "http://example.com http://example.com/.../foo //foo"
+    );
+}
+
 #[test]
 #[cfg_attr(
     not(target_os = "linux"),