bump dev dependencies to latest Ruby 3.0-compatible versions

Bump bundler (>= 2.5.23), debug (>= 1.11.1), and rubocop (~> 1.86.0)
to the latest versions that still support Ruby 3.0. Verified with
bundle exec rake on Ruby 3.0, 3.1, 3.2, 3.3, 3.4, and 4.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kzkn

Gemfile

@@ -4,12 +4,12 @@ source "https://rubygems.org"
 gemspec
 
 # Development dependencies
-gem "bundler", ">= 1.15"
-gem "debug", ">= 1.0.0"
+gem "bundler", ">= 2.5.23"
+gem "debug", ">= 1.11.1"
 gem "guard-rspec", "~> 4.0"
 gem "rake", "~> 13.0"
 gem "rspec", "~> 3.0"
 gem "rspec_junit_formatter", "~> 0.6.0"
-gem "rubocop", "~> 1.69.2"
+gem "rubocop", "~> 1.86.0"
 gem "simplecov", "~> 0.22.0"
 gem "simplecov-cobertura", "~> 3.1"