fix: extract postcode for vanoord and vanherk scrapers

Van Oord: postcode is in the first .elementor-heading-title on detail pages.
Van Herk: postcode extracted via regex from <title> tag; also pick up kamers
and energielabel from the features list which were previously ignored.
Test output now includes woonoppervlak and energielabel fields.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_adapters.py

@@ -23,4 +23,4 @@ if __name__ == "__main__":
     listings = ADAPTER()
     print(f"Got {len(listings)} listings\n")
     for l in listings:
-        print(f"  {l.adres}, {l.postcode}, {l.stad} — €{l.prijs} — {l.kamers} rooms — {l.url}")
+        print(f"  {l.adres}, {l.postcode}, {l.stad} — €{l.prijs} — {l.kamers} rooms — {l.woonoppervlak}m2 — {l.energielabel} — {l.url}")