Add `Append` method to `AllQueries`

gemma/gemma.h

@@ -60,6 +60,8 @@ struct PerQuery {
 
 // Array of `PerQuery`. Referenced by `QBatch` and passed to `GenerateBatch`.
 struct AllQueries {
+  AllQueries() = default;
+
   // For `GenerateSingleT`: same prompt/pos, replicated for each KV cache.
   AllQueries(const PromptTokens& prompt, size_t pos, size_t prefix_end,
              const hwy::Span<KVCache>& kv_caches) {
@@ -97,6 +99,9 @@ struct AllQueries {
     }
   }
 
+  void Reserve(size_t size) { per_query_.reserve(size); }
+  void Append(const PerQuery& query) { per_query_.push_back(query); }
+
   size_t NumQueries() const { return per_query_.size(); }
 
   PerQuery& operator[](size_t query_idx) {