Node 24 and related upgrades

[kookster]

So many upgrades!

Node 24 related updates:

1. Source imports — added .js extensions (11 files)

• index.js, lib/wavefile-converter.js, lib/wavefile-creator.js, lib/wavefile-parser.js, lib/wavefile-reader.js, lib/wavefile-tag-editor.js,
  lib/wavefile-cue-editor.js, lib/mpeg-reader.js, lib/riff-file.js, lib/resampler/index.js, lib/parsers/binary/index.js, lib/parsers/write-string.js
• Required for native ESM module resolution (directory imports → /index.js)

2. package.json

• Added "type": "module" — enables native ES modules
• Updated engines from >=8 to >=18
• Replaced nyc with c8 (V8-native coverage, works with modern Node)
• Upgraded mocha from ^6.2.2 to ^11.0.0
• Upgraded typescript from ^3.7.4 to ^5.0.0
• Removed esm (broken on Node 24, native ESM replaces it)
• Removed codecov and mocha-lcov-reporter (deprecated)
• Updated all npm scripts for modern tooling

3. New files

• test/package.json — {"type": "commonjs"} keeps 129+ test files as CJS
• dist/package.json — {"type": "commonjs"} keeps UMD bundle as CJS

4. test/loader.js — removed esm package, uses Node 24's native require(esm) support

5. test/dist/from-scratch/12bit-from-scratch.js — removed esm usage for byte-data

6. bin/wavefile.js — converted to ESM imports (uses dist/wrapper.mjs)

Rollup upgrade from 1 -> 4

• rollup 1.x → 4.x
• @rollup/plugin-commonjs 11 → 29
• @rollup/plugin-node-resolve 6 → 16
• Replaced @ampproject/rollup-plugin-closure-compiler with @rollup/plugin-terser
• Removed IE10 polyfill wrapper and ES3 class check from test loader

Miscellaneous Clean-up!

Dead files from closure compiler removal:

• externs/ directory — only used by closure compiler, no longer referenced
• scripts/polyfills.js — IE10 Uint8Array polyfill, was injected by closure compiler's outputWrapper

Outdated CI configs:

• .travis.yml — tests Node 8/9/10/12 on Travis CI (Travis free tier for open source is gone)
• appveyor.yml — same, Windows CI for Node 8-12

Vulnerability fixes:

• jsdoc 3.x → 4.x fixes the taffydb vulnerability (3 of 8 vulns)
• npm audit fix alone fixes the serialize-javascript issue in mocha (2 vulns)

Minor:

• The .jshintrc sets "esversion": 6 — bump to 11 to match modern JS