ci: automatically test on all LTS node versions

[msimerson]

• automatically test on all LTS node versions (currently: 18, 20)
  • example for testing on extra versions (21)
• adds windows testing (win tests take ~30 seconds longer)
• replace codecov dependency (in package.json) with codecov-action (in GHA workflow)
  • has working config for codecov & coveralls (commented out)
• test: prefix mocha with npx
  • no need to declare dependency, gets installed automatically when tests are run
  • pairs nicely with test: replace mocha with node.js builtin #135

I'm happy to amend this PR in any way that suits the maintainer(s).

fixes #119

Previews

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[msimerson]

Is there anything I can do to nudge this along?

[mathiasbynens]

With these changes, you can no longer git clone + npm install to get everything you need to work offline. Please revert these changes.

[msimerson]

Will do. Done.

Food for thought:

• the codecov module is officially deprecated
• nyc is almost unsupported (last release on npm, 4 years ago).
  • nyc only supports es6 via babel transpilation to es5 😬
  • the bare-bones support is has received is from bcoe, the author of c8, which remains the future of JS coverage reporting, using node's built-in coverage features.
  • The GHA workflow uses nyc, for consistency
• the big coverage reporters (codecov, coveralls, etc.) are nudging everyone to move to GHA style processing
• the included GitHub action will report the coverage results in PRs
• moving the code coverage entirely to a GitHub Action improves the default install (npm -i), because 99.9% ¹ of the time, nobody benefits from installing dev modules they'll never use.
  • npm i output now is 28 MB: added 237 packages, and audited 238 packages
  • w/o nyc & codecov: 6.4M ./node_modules
  • w/o nyc, codecov, & mocha: 0M ./node_modules
• I don't know about you but many of my PRs come from folks that still greatly struggle with git, let alone running npm test.
• if mocha is installed globally on your machine (as may be the case for a developer who prefers it), running npx mocha will use the globally installed (via npm i -g) version. Not only does this work great offline, but it saves a lot of wasted developer time when doing installs and reinstalls of modules.
• (aside: mocha is my favorite test runner), removing mocha as a dep pairs nicely with test: replace mocha with node.js builtin #135

1. Made up statistic, but lets be honest: so few people used npm i --production that all 68 of us noticed when npm changed it to npm i --omit=dev