fix: add require 'time' for iso8601 method compatibility

Fixes NoMethodError on Time#iso8601 in Ruby versions that don't
auto-require the time library.

Author: yhk1038

lib/t_ruby/benchmark.rb

@@ -3,6 +3,7 @@
 require "benchmark"
 require "json"
 require "fileutils"
+require "time"
 
 module TRuby
   # Benchmark suite for T-Ruby performance measurement

lib/t_ruby/bundler_integration.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "fileutils"
+require "time"
 
 module TRuby
   # Integrates T-Ruby type packages with Bundler/RubyGems ecosystem

lib/t_ruby/doc_generator.rb

@@ -2,6 +2,7 @@
 
 require "json"
 require "fileutils"
+require "time"
 
 module TRuby
   # API Documentation Generator

lib/t_ruby/docs_badge_generator.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "time"
 require_relative "docs_example_verifier"
 
 module TRuby

lib/t_ruby/package_manager.rb

@@ -4,6 +4,7 @@
 require "fileutils"
 require "net/http"
 require "uri"
+require "time"
 
 module TRuby
   # Semantic version parsing and comparison