Node.js has moved forward by several major versions since our CI configuration was last updated, and this updates our CI test matrix to cover them. I've also added Dependabot for updating CI workflows, but not JS dependencies (we only want security updates for those).

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Bumps [actions/setup-node](https://github.com/actions/setup-node) from 3 to 4.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](actions/setup-node@v3...v4)

---
updated-dependencies:
- dependency-name: actions/setup-node
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Even though we started generating TypeScript types from the JSDoc a while back, it turns out `BufferedMetricsLogger` was getting exported as a *value* and not a type. That technically works in TS, but requires some weird syntax and is definitely not what you want. This changes up our imports and exports a bit to get the TypeScript compiler to do the right thing, and adds a basic test of the types to make sure we don't regress.

See #119.