feat: Mutex を定義 (#49)

* feat: `Mutex` クラスを定義

* chore: テストを追加

Author: tufusa

core/mutex.rbs

@@ -0,0 +1,13 @@
+class Mutex
+  def initialize: () -> void
+
+  def lock: () -> self
+
+  def unlock: () -> self
+
+  def try_lock: () -> bool
+
+  def locked?: () -> bool
+
+  def owned?: () -> bool
+end

test/mutex.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+mutex = Mutex.new
+
+mutex.lock
+
+mutex.unlock
+
+mutex.try_lock
+
+mutex.locked?
+
+mutex.owned?