Add support for access token authentication

[jclusso]

• Added ability to specify api_key or access_token at request time
• Fixed bug with yarn test [file] not running just that file because it was combined with tsd. Made them two separate tasks.
• Improved tests to catch errors when they don't instead of relying on mocha timeout to fail the test.
• Updated CI

[n-older]

Looks good apart from the Copilot suggestions.

[Copilot]

Pull Request Overview

This PR enhances authentication by adding support for access tokens and refines testing and CI configurations.

• Added support for specifying an accessToken (or apiKey) at request time.
• Refactored promise error handling in tests and separated type testing in package.json.
• Updated documentation and CI to reflect the new authentication options.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/verify.spec.js	Added .catch(done) to promise chains in tests for consistent error handling.
test/emailable.test-d.ts	Added a new test for the account endpoint accepting an apiKey parameter.
test/batches.spec.js	Adjusted promise chains, but redundant .catch(done) calls were introduced in status tests.
test/authentication.spec.js	Introduced comprehensive tests for different authentication mechanisms.
test/account.spec.js	Updated error handling with .catch(done) affixed to promise chains.
package.json	Split type tests into a separate task and updated package manager settings.
lib/emailable.js	Modified constructor to support a default apiKey and updated the account method to accept options.
lib/client.js	Implemented support for accessToken by merging it with apiKey and applied request filtering.
README.md	Revised authentication documentation to cover both apiKey and accessToken usage.
.github/workflows/ci.yml	Expanded the Node.js version matrix and added a step to run type definition tests.