Reduce gem package size by excluding non-essential files

Remove test/, sig/deps.rbs, CHANGELOG.md, CONTRIBUTING.md, SECURITY.md,
and UPGRADING.md from the packaged gem.

Author: sferik

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+
+- Exclude test files from gem package, reducing gem size by 50% (from 175 KB to 87 KB).
+
 ## [6.0.0] - 2026-03-16
 
 ### Changed

http.gemspec

@@ -26,10 +26,10 @@ Gem::Specification.new do |spec|
   spec.metadata["rubygems_mfa_required"] = "true"
 
   spec.files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
-    extras = %w[CHANGELOG.md CONTRIBUTING.md LICENSE.txt README.md SECURITY.md UPGRADING.md] << File.basename(__FILE__)
+    extras = %w[LICENSE.txt README.md sig/http.rbs] << File.basename(__FILE__)
 
     ls.readlines("\x0", chomp: true).select do |f|
-      f.start_with?("lib/", "test/", "sig/") || extras.include?(f)
+      f.start_with?("lib/") || extras.include?(f)
     end
   end