fix: handle optional primitive types in @TypeOf annotations

- Treat []const u8 as string primitive, not array (fixes ?[]const u8)
- Optional primitives generate ?T = null (e.g., ?[]const u8 = null)
- Added test for optional string type annotation

build.zig.zon

@@ -1,6 +1,6 @@
 .{
     .name = .pugz,
-    .version = "0.3.14",
+    .version = "0.3.15",
     .fingerprint = 0x822db0790e17621d, // Changing this has security and trust implications.
     .minimum_zig_version = "0.15.2",
     .dependencies = .{},