Fix: Hash @indices can grow larger than Int32::MAX bytes

fixes #15341

Co-authored-by: Johannes Müller <straightshoota@gmail.com>

src/hash.cr

@@ -830,7 +830,7 @@ class Hash(K, V)
 
   # The actual number of bytes needed to allocate `@indices`.
   private def indices_malloc_size(size)
-    size * @indices_bytesize
+    size.to_u64 * @indices_bytesize
   end
 
   # Reallocates `size` number of indices for `@indices`.