test: bring CLI coverage to 100% and enforce it

[Tony133]

Proposal:

Follow-up to #913. Now that suite-runner.js actually runs the tests, c8 reports real numbers for the CLI sources, and they were around 87%. This brings every file under *.js and lib/** to 100% statements / branches / functions / lines, and adds a .c8rc.json with check-coverage: true so npm test fails if it drops.

The c8 report is also scoped to the shipped sources: test/, templates/, examples/ and suite-runner.js are excluded, since they are fixtures and test infrastructure rather than CLI code.

New and extended tests:

• generate-readme, generate-swagger, print-plugins, print-routes, generate, generate-plugin, eject, cli: the cli() paths and the require.main === module blocks are exercised by spawning the scripts as child processes (c8 follows children via NODE_V8_COVERAGE), so process.exit paths are tested for real. Error paths in generate() use proxyquire to fail generify and node:fs.
• util.test.js: exit, requireModule*, requireFastifyForModule failure, showHelpForCommand with an unknown command, isKubernetes.
• start-extra.test.js: missing file parameter, fastify not loadable, --address, --trust-proxy-enabled (verified through request.ip), the err branch of the close-with-grace handler. The two is-docker mocks in start.test.js now cover both module shapes (CJS function and ESM { default }).
• watch-unit.test.js: lib/watch/index.js driven with fake chokidar / child_process.fork (restart on change, verbose logging, ready emitted once, error → stop, uncaughtException → restart).
• watch-fork.test.js: lib/watch/fork.js forked for real (app crash, EADDRINUSE, graceful shutdown, forced exit after the close timeout, shutdown before the server is up). Each test has a timeout and kills its child on teardown, so a stuck child fails the test instead of hanging the suite.
• print-plugins / print-routes: the skip under coverage is gone. It was needed with nyc, which instrumented the sources and changed the printed function bodies; c8 uses native V8 coverage and does not touch the code (verified with NODE_V8_COVERAGE set).

Bugs found on the way:

• node eject.js --esm crashed: the standalone entry point called cli() without arguments. Now cli(process.argv.slice(2)).
• In generate.js, a failing npm init -y threw synchronously inside the generify callback and escaped the promise: an uncaught exception instead of log('error') + exit 1. It is now caught and rejected.

Dead code removed:

• util.js: the moduleSupport check (Node < 14). semver is no longer needed at runtime and moves to devDependencies (tests still use it).
• start.js: the "debug mode not compatible with Node < 6" branch.
• lib/watch/index.js: the childs.length !== 0 branch in the change handler — at most one child is ever in the array.
• lib/watch/fork.js: the try/catch around fastify.ready() after listen() already succeeded; a rejection there is handled by main().catch, with the same exit code.
• generate-readme.js: stop(error) was only ever called without an argument.
• args.js: commandLineArguments['--'] || [] — '--' is always populated with populateRest: true.
• lib/parse-args.js: token.original is never set on positional tokens.
• pkg.scripts = Object.assign(pkg.scripts || {}, …) → object spread, same semantics without the branch.

Based on #913 — merge that one first.

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Screenshot Test Coverage 100%

see also here: https://github.com/fastify/fastify-cli/actions/runs/34277129667/job/102232798581?pr=916#step:5:589