[Minor] Add is_avalanching type hint

src/libserver/css/css_property.hxx

@@ -141,6 +141,7 @@ namespace std {
 template<>
 class hash<rspamd::css::css_property> {
 public:
+	using is_avalanching = void;
 	/* Mix bits to provide slightly better distribution but being constexpr */
 	constexpr size_t operator() (const rspamd::css::css_property &prop) const {
 		std::size_t key = 0xdeadbeef ^static_cast<std::size_t>(prop.type);

src/libserver/css/css_rule.hxx

@@ -73,6 +73,7 @@ namespace std {
 template<>
 class hash<rspamd::css::css_rule> {
 public:
+	using is_avalanching = void;
 	constexpr auto operator()(const rspamd::css::css_rule &rule) const -> auto {
 		return hash<rspamd::css::css_property>()(rule.get_prop());
 	}

src/libserver/css/css_selector.hxx

@@ -106,6 +106,7 @@ namespace std {
 template<>
 class hash<rspamd::css::css_selector> {
 public:
+	using is_avalanching = void;
 	auto operator() (const rspamd::css::css_selector &sel) const -> std::size_t {
 		if (sel.type == rspamd::css::css_selector::selector_type::SELECTOR_TAG) {
 			return static_cast<std::size_t>(std::get<tag_id_t>(sel.value));

src/libutil/cxx/hash_util.hxx

@@ -80,6 +80,7 @@ struct smart_str_equal {
 
 struct smart_str_hash {
 	using is_transparent = void;
+	using is_avalanching = typename ankerl::unordered_dense::hash<std::string_view>::is_avalanching;
 	auto operator()(const std::string &a) const {
 		return ankerl::unordered_dense::hash<std::string>()(a);
 	}