optimize blocks fetching from cache

apps/explorer/lib/explorer/chain.ex

@@ -1155,9 +1155,7 @@ defmodule Explorer.Chain do
 
     if block_type == "Block" && !paging_options.key do
       if BlocksCache.enough_elements?(paging_options.page_size) do
-        cached_blocks = BlocksCache.blocks()
-
-        Enum.slice(cached_blocks, 0, paging_options.page_size)
+        BlocksCache.blocks(paging_options.page_size)
       else
         elements = fetch_blocks(block_type, paging_options, necessity_by_association)
 

apps/explorer/lib/explorer/chain/blocks_cache.ex

@@ -56,12 +56,15 @@ defmodule Explorer.Chain.BlocksCache do
     end)
   end
 
-  def blocks do
+  def blocks(number \\ nil) do
     numbers = block_numbers()
 
+    number = if is_nil(number), do: Enum.count(numbers), else: number
+
     numbers
     |> Enum.sort()
     |> Enum.reverse()
+    |> Enum.slice(0, number)
     |> Enum.map(fn number ->
       ConCache.get(@cache_name, number)
     end)