hash.c: add __pat_values() for pattern matching optimization

Add Hash#__pat_values(keys) that returns an array of values if all
keys exist, or false if any key is missing. This replaces per-key
key?() + []() calls (2N hash lookups) with a single method call
(N hash lookups). The compiler generates __pat_values() followed by
array indexing to extract each value for pattern matching.

Co-authored-by: Claude <noreply@anthropic.com>

src/hash.c

@@ -2042,6 +2042,36 @@ mrb_hash_compact(mrb_state *mrb, mrb_value hash)
   return hash;
 }
 
+/*
+ * Internal method for pattern matching key check + value extraction.
+ * Returns an array of values if all keys exist, false otherwise.
+ *
+ *   {a: 1, b: 2}.__pat_values([:a, :b])  #=> [1, 2]
+ *   {a: 1}.__pat_values([:a, :b])         #=> false
+ */
+static mrb_value
+mrb_hash_pat_values(mrb_state *mrb, mrb_value hash)
+{
+  mrb_value keys;
+  mrb_get_args(mrb, "A", &keys);
+
+  const mrb_value *ary = RARRAY_PTR(keys);
+  mrb_int klen = RARRAY_LEN(keys);
+  struct RHash *h = mrb_hash_ptr(hash);
+  mrb_value result = mrb_ary_new_capa(mrb, klen);
+  int ai = mrb_gc_arena_save(mrb);
+
+  for (mrb_int i = 0; i < klen; i++) {
+    mrb_value val;
+    if (!h_get(mrb, h, ary[i], &val)) {
+      return mrb_false_value();
+    }
+    mrb_ary_push(mrb, result, val);
+    mrb_gc_arena_restore(mrb, ai);
+  }
+  return result;
+}
+
 /*
  * Internal method for pattern matching **rest.
  * Returns a new hash excluding keys in the given array.
@@ -2314,6 +2344,7 @@ mrb_init_hash(mrb_state *mrb)
   mrb_define_method_id(mrb, h, MRB_SYM(rassoc),          mrb_hash_rassoc,      MRB_ARGS_REQ(1));
   mrb_define_method_id(mrb, h, MRB_SYM(__merge),         mrb_hash_merge_m,     MRB_ARGS_REQ(1));
   mrb_define_method_id(mrb, h, MRB_SYM(__compact),       mrb_hash_compact,     MRB_ARGS_NONE()); /* implementation of Hash#compact! */
+  mrb_define_method_id(mrb, h, MRB_SYM(__pat_values),    mrb_hash_pat_values,  MRB_ARGS_REQ(1)); /* for pattern matching keys */
   mrb_define_method_id(mrb, h, MRB_SYM(__except),        mrb_hash_except_keys, MRB_ARGS_REQ(1)); /* for pattern matching **rest */
 }
 #undef lesser