feat!: migrate mingw to custom resources

[damacus]

Summary

• Removes mingw::default recipe and node['msys2'] attributes; the cookbook now ships custom resources only.
• Adds source_url / checksum properties to msys2_package and mingw_get to replace the dropped node attributes.
• Modernizes all three resources (mingw_get, msys2_package, mingw_tdm_gcc) with provides, frozen_string_literal, unified_mode true, missing :remove action on mingw_tdm_gcc, and Mingw::Helpers included via action_class.
• Replaces seven_zip_archive with built-in remote_file + archive_file (drops the seven_zip cookbook dependency).
• Bumps chef_version floor to >= 16.0.
• Consolidates Kitchen for Windows-only: deletes kitchen.dokken.yml and kitchen.global.yml; rewrites kitchen.yml for Vagrant on Windows Server 2019/2022 and kitchen.exec.yml for CI on windows-latest (Server 2022).
• Replaces serverspec dirs with full InSpec profiles under test/integration/<suite>/{inspec.yml,controls/} and replaces fixture cookbooks with test/cookbooks/test/recipes/<suite>.rb.
• Pins all sous-chefs reusable workflows to @6.0.0, swaps actionshub/chef-install for sous-chefs/.github/.github/actions/install-workstation@6.0.0, and adds slack_bot_token / slack_channel_id secrets to release.yml.
• Aligns CI matrix instance regex to the dashed Kitchen-normalized name (msys2-tools64).

Breaking changes

• mingw::default recipe removed.
• node['msys2']['url'] and node['msys2']['checksum'] removed; use msys2_package's source_url and checksum properties.
• seven_zip cookbook is no longer a dependency.
• chef_version minimum is now >= 16.0.

See migration.md for upgrade examples.

Verification done in-session

• cookstyle — 21 files inspected, 0 offenses.
• chef exec rspec --format documentation — 24 examples, 0 failures. Every resource has step_into coverage; helpers have unit tests.
• KITCHEN_LOCAL_YAML=kitchen.exec.yml kitchen list — all 4 instances visible (default-windows-2022, tools32-windows-2022, tools64-windows-2022, msys2-tools64-windows-2022).
• Final structural audit (ls -R) confirms recipes/, attributes/, files/, libraries/_helper.rb, test/fixtures/, and test/integration/*/serverspec/ are all gone.

Verification deferred to CI

This is a Windows-only cookbook and the local dev host is macOS, so kitchen test cannot run from the dev session. CI on windows-latest (using KITCHEN_LOCAL_YAML=kitchen.exec.yml) is the integration verifier — that's the gate this PR needs to clear before merge.

Test plan

• lint-unit workflow passes (cookstyle + ChefSpec on the org runner)
• integration matrix passes for all 4 suites on windows-latest:
  • default (smoke MSYS2 base + base-devel)
  • tools32 (legacy 32-bit TDM-GCC + mingw_get packages)
  • tools64 (legacy 64-bit TDM-GCC + mingw_get packages)
  • msys2-tools64 (MSYS2 64-bit MinGW toolchain)
• prevent-file-change passes
• On merge, release-please opens a release PR bumping mingw to 5.0.0 (driven by feat!: / BREAKING CHANGE)

[github-actions]

Slowest examples

Top 10 slowest examples (0.25 seconds, 51.86% of total time)

Example	Description	Time in seconds
spec/unit/resources/get_spec.rb:16	mingw_get installing a package is expected to create directory "C:\mingw32.cache"	0.02981
spec/unit/resources/msys2_package_spec.rb:18	msys2_package installing a package with defaults is expected to extract archive_file "extract msys2 base archive to C:\msys2.cache"	0.02833
spec/unit/resources/msys2_package_spec.rb:24	msys2_package installing a package with defaults is expected to run execute "installing base-devel"	0.02695
spec/unit/resources/msys2_package_spec.rb:41	msys2_package installing with a custom base archive is expected to create remote_file "cache msys2 base to C:\msys2.cache"	0.02603
spec/unit/resources/tdm_gcc_spec.rb:30	mingw_tdm_gcc installing 32-bit TDM-GCC is expected to install mingw_get "install binutils-bin=2.25.1 at C:\mingw32"	0.02588
spec/unit/resources/get_spec.rb:17	mingw_get installing a package is expected to create remote_file "cache mingw-get to C:\mingw32.cache"	0.02554
spec/unit/resources/tdm_gcc_spec.rb:19	mingw_tdm_gcc installing 64-bit TDM-GCC is expected to extract archive_file "extract gcc-5.1.0-tdm64-1-core.tar to C:\mingw64"	0.02489
spec/unit/resources/msys2_package_spec.rb:19	msys2_package installing a package with defaults is expected to create directory "C:\msys2\bin"	0.02426
spec/unit/resources/msys2_package_spec.rb:16	msys2_package installing a package with defaults is expected to create directory "C:\msys2.cache"	0.02401
spec/unit/resources/msys2_package_spec.rb:22	msys2_package installing a package with defaults is expected to create template "C:\msys2\etc\profile.d\custom_prefix.sh"	0.02381