fmt: fix pos of added imports (#8931)

vlib/v/fmt/fmt.v

@@ -236,6 +236,9 @@ pub fn (mut f Fmt) mod(mod ast.Module) {
 	}
 	f.attrs(mod.attrs)
 	f.writeln('module $mod.short_name\n')
+	if f.import_pos == 0 {
+		f.import_pos = f.out.len
+	}
 }
 
 pub fn (mut f Fmt) mark_types_import_as_used(typ table.Type) {

vlib/v/fmt/tests/import_auto_added_expected.vv

@@ -0,0 +1,7 @@
+module main
+
+import time
+
+fn main() {
+	curr_time := time.now()
+}

vlib/v/fmt/tests/import_auto_added_input.vv

@@ -0,0 +1,5 @@
+module main
+
+fn main() {
+	curr_time := time.now()
+}