refactor: migrate apt to custom resources

[damacus]

Summary

• replace the legacy recipe and attributes entrypoints with custom resources for base apt config, apt-cacher client, apt-cacher-ng, and unattended upgrades
• move cookbook usage into test cookbooks, add resource docs, and convert the unit and integration coverage to the new resource layout
• modernize the supported platform metadata and Kitchen configuration around the Debian and Ubuntu test matrix

Testing

• cookstyle .
• chef exec rspec --format documentation
• KITCHEN_LOCAL_YAML=kitchen.dokken.yml kitchen test default-debian-12 --destroy=always

[github-actions]

Slowest examples

Top 10 slowest examples (0.74 seconds, 62.32% of total time)

Example	Description	Time in seconds
spec/unit/resources/config_spec.rb:18	apt_config is expected to create file "/var/lib/apt/periodic/update-success-stamp"	0.1573
spec/unit/resources/config_spec.rb:17	apt_config is expected to periodic apt_update "periodic"	0.07851
spec/unit/resources/unattended_upgrades_spec.rb:20	apt_unattended_upgrades is expected to render file "/etc/apt/apt.conf.d/20auto-upgrades"	0.07775
spec/unit/resources/cacher_client_spec.rb:18	apt_cacher_client without a cache server is expected to delete file "/etc/apt/apt.conf.d/01proxy"	0.07634
spec/unit/resources/config_spec.rb:22	apt_config is expected to render file "/etc/apt/apt.conf.d/10recommends"	0.07063
spec/unit/resources/cacher_ng_spec.rb:21	apt_cacher_ng is expected to enable service "apt-cacher-ng"	0.06349
spec/unit/resources/unattended_upgrades_spec.rb:21	apt_unattended_upgrades is expected to render file "/etc/apt/apt.conf.d/50unattended-upgrades"	0.05883
spec/unit/resources/cacher_ng_spec.rb:17	apt_cacher_ng is expected to install package "apt-cacher-ng"	0.05624
spec/unit/resources/cacher_ng_spec.rb:18	apt_cacher_ng is expected to create directory "/tmp/apt-cacher"	0.05424
spec/unit/resources/config_spec.rb:20	apt_config is expected to create directory "/var/cache/local/preseeding"	0.05347