Rename test directory from model_context_protocol to mcp

Follow-up to #24.

The directory structure of the product code and test code is expected to match.

test/model_context_protocol/configuration_test.rb

@@ -1,65 +0,0 @@
-# frozen_string_literal: true
-
-require "test_helper"
-
-module MCP
-  class ConfigurationTest < ActiveSupport::TestCase
-    test "initializes with a default no-op exception reporter" do
-      config = Configuration.new
-      assert_respond_to config, :exception_reporter
-
-      # The default reporter should be callable but do nothing
-      exception = StandardError.new("test error")
-      server_context = { test: "context" }
-
-      # Should not raise any errors
-      config.exception_reporter.call(exception, server_context)
-    end
-
-    test "allows setting a custom exception reporter" do
-      config = Configuration.new
-      reported_exception = nil
-      reported_context = nil
-
-      config.exception_reporter = ->(exception, server_context) do
-        reported_exception = exception
-        reported_context = server_context
-      end
-
-      test_exception = StandardError.new("test error")
-      test_context = { foo: "bar" }
-
-      config.exception_reporter.call(test_exception, test_context)
-
-      assert_equal test_exception, reported_exception
-      assert_equal test_context, reported_context
-    end
-
-    test "initializes with default protocol version" do
-      config = Configuration.new
-      assert_equal Configuration::DEFAULT_PROTOCOL_VERSION, config.protocol_version
-    end
-
-    test "allows setting a custom protocol version" do
-      config = Configuration.new
-      custom_version = "2025-03-27"
-      config.protocol_version = custom_version
-      assert_equal custom_version, config.protocol_version
-    end
-
-    test "merges protocol version from other configuration" do
-      config1 = Configuration.new(protocol_version: "2025-03-27")
-      config2 = Configuration.new(protocol_version: "2025-03-28")
-      config3 = Configuration.new
-
-      merged = config1.merge(config2)
-      assert_equal "2025-03-28", merged.protocol_version
-
-      merged = config1.merge(config3)
-      assert_equal "2025-03-27", merged.protocol_version
-
-      merged = config3.merge(config1)
-      assert_equal "2025-03-27", merged.protocol_version
-    end
-  end
-end