feat(node): add node implementation

[edlng]

Summary

This adds a Node.js library for generating Amazon ElastiCache IAM authentication tokens. It supports serverless caches and node-based replication groups through a typed API and a reusable token provider.

The change also adds Node CI, package validation, examples, documentation, and focused coverage for signing, configuration resolution, credential refresh, validation, and published-package exports.

What's in it

Area	Change
node/src	Adds SigV4 token generation, typed options, public error types, and ElastiCacheIAMAuthTokenProvider.
node/examples	Adds standalone token-generation and Valkey GLIDE integration examples.
node/test	Covers known-answer signatures, target and user validation, region precedence, credential failures and rotation, provider lifecycle, and package exports.
node/package.json	Adds the Node 22+ ESM package, AWS signing dependencies, build/test scripts, and package metadata.
.github/workflows/node.yml	Tests Node 22 and 24 on Ubuntu and Windows with lint, formatting, typecheck, tests, build, and package validation.
.github/dependabot.yml	Adds weekly npm dependency updates for the Node package.
README.md, node/README.md	Documents Node installation, token generation, provider usage, examples, and the Python/Node package split.

Design decisions

• ElastiCacheIAMAuthTokenProvider.create() resolves the region before returning so missing configuration fails during setup. The synchronous constructor retains the error and reports it from getToken().
• The provider retains its signing region but resolves credentials for every token request so rotated SSO, assumed-role, container, and instance credentials are picked up.
• The Node CLI and release workflow were removed. The Node package is library-only; the Python package remains the command-line interface. Let me know if we need it, I can add this back.

Tests

• npm run lint — passed.
• npm run typecheck — passed.
• npm test — passed, 56 tests.
• npm run format:check — currently fails because node/src/errors.ts contains trailing whitespace.

Not in this PR

• Publishing or release automation for the private Node package.
• A Node command-line interface. Do we need one for Node? Let me know if we need it, I can add this back.

Signed-off-by: Edward Liang liawedwa@amazon.com

[mwaisaida-13]

Really solid port, 1:1 with the Python library on the parity contract. Four small comments inline (centralize the Node version matrix, add macOS to CI, swap the GLIDE example for a client without built-in IAM auth, drop examples from files). One more: please add node/CHANGELOG.md in Keep-a-Changelog format with an Unreleased entry, since versions and releases are per-language. Thank you!

P.S. no need for the CLI :)

[mwaisaida-13]

Thanks, LGTM 🚀