Fix single-line brace formatting to preserve internal whitespace

The formatter now calculates and passes explicit leading and trailing whitespace around expression content to the `_brace` method. This ensures correct rendering of single-line expressions that include braces.

server/src/tools/formatter.py

@@ -26,6 +26,8 @@ class NxFormatter(BaseFormatter):
                 formatted += [line]
 
         if expr.pos[0] == expr.end_pos[0]:
-            return self._brace(formatted)
+            space_before = expr.children[0].pos[1] - expr.pos[1] - 1
+            space_after = expr.end_pos[1] - expr.children[-1].end_pos[1] - 1
+            return self._brace(formatted, (space_before, space_after))
 
         return ["{"] + self._indent(formatted, self.opts.indent) + ["}"]