iceberg: persist namespace properties for create/get (#8276)

* iceberg: persist namespace properties via s3tables metadata

* iceberg: simplify namespace properties normalization

* s3tables: broaden namespace properties round-trip test

* adjust logs

* adjust logs

weed/s3api/iceberg/iceberg_namespace_properties_test.go

@@ -0,0 +1,29 @@
+package iceberg
+
+import "testing"
+
+func TestNormalizeNamespacePropertiesNil(t *testing.T) {
+	properties := normalizeNamespaceProperties(nil)
+	if properties == nil {
+		t.Fatalf("normalizeNamespaceProperties(nil) returned nil map")
+	}
+	if len(properties) != 0 {
+		t.Fatalf("normalizeNamespaceProperties(nil) length = %d, want 0", len(properties))
+	}
+}
+
+func TestNormalizeNamespacePropertiesReturnsInputWhenSet(t *testing.T) {
+	input := map[string]string{
+		"owner": "analytics",
+	}
+
+	properties := normalizeNamespaceProperties(input)
+	if properties["owner"] != "analytics" {
+		t.Fatalf("normalized properties value = %q, want %q", properties["owner"], "analytics")
+	}
+
+	input["owner"] = "updated"
+	if properties["owner"] != "updated" {
+		t.Fatalf("normalizeNamespaceProperties should reuse the input map when non-nil")
+	}
+}