feat: support @import type expressions in @TypeOf annotations

- Parser accepts '=' separator in addition to ':' for @TypeOf syntax
- New import_type and is_optional fields in TypeInfo
- Dotted field access (user.name) preserved as real Zig dot-access for import types
- Optional import types use .? unwrap (data.user.?.name)
- Field extraction collapses user.name to user when user has @import type
- Added zig_codegen tests to integration test suite
- Fixed stale test signatures in zig_codegen.zig

build.zig.zon

@@ -1,6 +1,6 @@
 .{
     .name = .pugz,
-    .version = "0.3.13",
+    .version = "0.3.14",
     .fingerprint = 0x822db0790e17621d, // Changing this has security and trust implications.
     .minimum_zig_version = "0.15.2",
     .dependencies = .{},