Require the test helper directly instead of injecting it via ruby_opts

[hsbt]

CI on Windows head and mswin fails with cannot load such file -- core_assertions (#55, ruby/rubygems#9782). The root cause is that ruby/ruby's gem_prelude.rb no longer requires bundler/setup implicitly, so the helper injected through t.ruby_opts << "-rhelper" runs before Bundler activates the git-sourced test-unit-ruby-core gem.

This drops the ruby_opts injection and requires the helper from the test files with require_relative, deferring it until after bundler/setup has run.

Fixes #55

Generated with Claude Code

[Copilot]

Pull request overview

Updates the test harness to avoid relying on Rake::TestTask RUBYOPT injection for loading the test helper, addressing Windows CI failures where core_assertions cannot be loaded before Bundler has activated git-sourced gems.

Changes:

• Remove t.ruby_opts << "-rhelper" (and the extra test/lib load path) from the Rakefile test task.
• Require the shared test helper directly from affected test entrypoints via require_relative.
• Ensure the helper (which pulls in test/unit and core_assertions) is loaded after Bundler setup in the test process.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
test/drb/test_drbobject.rb	Requires the shared test helper via require_relative instead of directly requiring test/unit.
test/drb/test_acl.rb	Requires the shared test helper via require_relative to defer helper loading until after Bundler is active.
test/drb/drbtest.rb	Requires the shared test helper so all tests that depend on drbtest inherit the correct setup.
Rakefile	Drops test helper loading via ruby_opts injection (and the extra test/lib load path).

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[hsbt]

As a side note, test/lib/helper.rb lives outside test/drb because that layout was needed to sync with ruby/ruby. That reason is gone now, so it might be better to move the helper into the same directory as the tests.