chore: remove SimpleCov code-coverage tooling

[tas50]

What

Removes SimpleCov and everything that existed only to serve it:

• gem "simplecov", "~> 0.22" from the :test group in Gemfile
• require "simplecov" and the SimpleCov.start block (add_filter, add_group, enable_coverage :branch) from spec/spec_helper.rb
• the coverage artifact path from .gitignore

That is the whole footprint. There was no minimum_coverage enforcement, no COVERAGE env-var branching, no coverage rake task, and no CI step that uploaded or reported coverage, so there was nothing else to take out.

What this does not touch

The YARD doc and doc_coverage rake tasks stay. doc_coverage runs yard stats --list-undoc — that is documentation coverage, not code coverage, and it is the thing that keeps lib/ at 100% documented. Both still work:

$ bundle exec rake -T
rake doc                    # Generate YARD Documentation
rake doc_coverage           # List anything in lib/ that is still undocumented

$ bundle exec rake doc_coverage
yard stats --list-undoc
Modules:         3 (    0 undocumented)
Classes:         1 (    0 undocumented)
Constants:       3 (    0 undocumented)
Attributes:      0 (    0 undocumented)
Methods:        30 (    0 undocumented)
 100.00% documented

Also untouched: the sentence in CONTRIBUTING.md about there being "no automated coverage of the Windows path yet". That is a statement about which platforms the suite exercises, not about the measurement tool, and it is still true.

Why

Nothing gated on the numbers. No CI job published a report, no threshold failed a build, and the only consumer was whoever opened coverage/index.html locally. What it did cost was a development dependency and a Renovate stream for a gem that measures the suite rather than testing it.

The recent test work stands on its own: this removes the measurement, not a single test.

Verification

Example count is unchanged — this was verified against origin/main before the change and again after:

before:  152 examples, 0 failures   (Line 100.0% (226/226), Branch 92.74% (115/124))
after:   152 examples, 0 failures

Lint, with Cookstyle 9.0.0 / RuboCop 1.90.0 (bundle updated first so it matches what CI resolves, since Gemfile.lock is gitignored):

$ bundle exec cookstyle --chefstyle
Inspecting 5 files
.....

5 files inspected, no offenses detected

Greps, run from the repo root excluding .git, both return nothing:

$ grep -rin 'simplecov' . --exclude-dir=.git   # no matches
$ grep -rn 'COVERAGE' . --exclude-dir=.git     # no matches

Notes

• No CHANGELOG entry mentions simplecov — I checked (grep -in 'simplecov\|coverage' CHANGELOG.md is empty). SimpleCov was added after the 0.13.1 release, so it never reached published release history. Nothing was edited in that release-please-managed file.
• chore(deps): update dependency simplecov to v1 #96 (renovate/simplecov-1.x) is made obsolete by this change and should be closed once this lands. It has in fact already been closed independently, so no action is likely needed — but if Renovate reopens it, close it rather than trying to fix it. It was red because simplecov 1.x requires Ruby > 3.1 and this gemspec supports 3.1.
• fix: load packages whose run hook is a run file in the package root #103 (fix: the hab svc load run-hook detection) has already merged into main; this branch is cut from the resulting aac0970. It touched only lib/kitchen/provisioner/habitat.rb and spec/kitchen/provisioner/habitat/run_command_spec.rb — not spec/spec_helper.rb, the Gemfile, or the Rakefile — so there is no overlap and no merge-order constraint between the two.