Use new mochify, update dependencies, drop old node

[mantoni]

Purpose (TL;DR) - mandatory

• Update all dependencies.
• Update GitHub actions.
• Drop node 12 and 14
• Support node 18 and 20

Caveat

I could not use ESBuild as the mochify bundler because it ran into a dual package hazard issue with sinon.

• Browserify looks at the browser field in package.json and decides to load ./lib/sinon.js.
• ESBuild checks the exports and chooses the browser field from there, which points to ./pkg/sinon-esm.js.

I can override that behaviour with conditions, but then ESBuild complains that it cannot resolve assert, while Browserify will happily shim that dependency transparently.

Update: Consuming this with ESBuild doesn't work due to sinonjs/sinon#2519. Reverting this change makes it work again. ¯\(ツ)/¯

How to verify - mandatory

1. Check out this branch
2. npm install
3. npm run lint
4. npm test
5. npm run test-cloud

Checklist for author

• npm run lint passes
• References to standard library functions are cached.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3ae4bd2) 100.00% compared to head (b83fd24) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #132   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          137       137           
=========================================
  Hits           137       137           

Flag	Coverage Δ
unit	100.00% <ø> (ø)

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