perf(sandbox): make register_caches sleep configurable

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 0.4.9
+
+## Performance
+
+- perf(sandbox): make `Cache.SandboxRegistry.register_caches/2` post-register sleep configurable via `Cache.Config.sandbox_sleep_ms/0` (`config :elixir_cache, :sandbox_sleep_ms, 50`). Default is unchanged (50 ms). Test suites that don't need the sleep can set it to `0` in `config/test.exs` to save ~50 ms per cache registered per test — material on apps with many cache modules.
+
 # 0.4.8
 
 ## Bug Fixes

lib/cache/config.ex

@@ -0,0 +1,9 @@
+defmodule Cache.Config do
+  @moduledoc false
+
+  @app :elixir_cache
+
+  def sandbox_sleep_ms do
+    Application.get_env(@app, :sandbox_sleep_ms, 50)
+  end
+end

lib/cache/sandbox_registry.ex

@@ -5,7 +5,6 @@ defmodule Cache.SandboxRegistry do
   More details soon...
   """
 
-  @sleep_for_sync 50
   @registry :elixir_cache_sandbox
   @keys :duplicate
 
@@ -38,7 +37,7 @@ defmodule Cache.SandboxRegistry do
         {:error, :registry_not_started} -> raise_not_started!()
       end
 
-    Process.sleep(@sleep_for_sync)
+    Process.sleep(Cache.Config.sandbox_sleep_ms())
 
     res
   end

mix.exs

@@ -4,7 +4,7 @@ defmodule ElixirCache.MixProject do
   def project do
     [
       app: :elixir_cache,
-      version: "0.4.8",
+      version: "0.4.9",
       elixir: "~> 1.11",
       start_permanent: Mix.env() == :prod,
       description: