fix: harden gem source commands

[damacus]

Summary

• Escape packagecloud gem source add/remove commands
• Replace grep and xargs gem-source removal with Ruby-native URI matching
• Update resource specs for the new Ruby block removal path

Verification

• cookstyle resources/repo.rb spec/unit/resources/repo_spec.rb
• /opt/chef-workstation/embedded/bin/rspec spec/unit/resources/repo_spec.rb --format progress

[github-actions]

Slowest examples

Top 10 slowest examples (0.54 seconds, 67% of total time)

Example	Description	Time in seconds
spec/unit/resources/repo_spec.rb:42	packagecloud_repo on ubuntu with default properties is expected not to run execute "apt-key-add-test_repo"	0.06533
spec/unit/resources/repo_spec.rb:71	packagecloud_repo on almalinux with rpm defaults is expected to create template "/etc/yum.repos.d/test_repo.repo"	0.06398
spec/unit/resources/repo_spec.rb:38	packagecloud_repo on ubuntu with default properties is expected to install package "wget"	0.06097
spec/unit/resources/repo_spec.rb:104	packagecloud_repo with gem source with action :add is expected to run execute "install packagecloud test/repo repo as gem source"	0.05416
spec/unit/resources/repo_spec.rb:84	packagecloud_repo on almalinux with action :remove is expected to delete file "/etc/yum.repos.d/test_repo.repo"	0.05337
spec/unit/resources/repo_spec.rb:119	packagecloud_repo with gem source with action :remove is expected to run ruby_block "remove packagecloud test/repo repo as gem source"	0.04985
spec/unit/resources/repo_spec.rb:41	packagecloud_repo on ubuntu with default properties is expected to create template "/etc/apt/sources.list.d/test_repo.list"	0.04946
spec/unit/resources/repo_spec.rb:43	packagecloud_repo on ubuntu with default properties is expected not to run execute "apt-get-update-test_repo"	0.0484
spec/unit/resources/repo_spec.rb:40	packagecloud_repo on ubuntu with default properties is expected to install package "lsb-release"	0.04825
spec/unit/resources/repo_spec.rb:39	packagecloud_repo on ubuntu with default properties is expected to install package "apt-transport-https"	0.0476