Remove duplicates from the combined header list of the runtime header…

…s and compile time headers (#2)

* Remove duplicates from the combined header list of the runtime headers and compile time headers

* Feedback changes

lib/http_client_builder.ex

@@ -96,7 +96,8 @@ defmodule HttpClientBuilder do
 
         headers =
           if unquote(client_opts)[:runtime_headers_getter] do
-            unquote(client_opts)[:runtime_headers_getter].() ++ compile_time_headers
+            (unquote(client_opts)[:runtime_headers_getter].() ++ compile_time_headers)
+            |> dedup_headers()
           else
             compile_time_headers
           end
@@ -114,6 +115,12 @@ defmodule HttpClientBuilder do
         base_url <> url_or_path <> query
       end
 
+      defp dedup_headers(headers) do
+        headers
+        |> Enum.reduce(%{}, fn {k, v}, acc -> Map.put(acc, k, v) end)
+        |> Map.to_list()
+      end
+
       defoverridable get: 2, post: 2, put: 2, delete: 2, patch: 2, do_request: 3, build_url: 2
     end
   end