Build using `ts-bridge` rather than `tsc` directly

Currently we output a build in CommonJS format. We should support ESM as well.

We can do this by switching to `ts-bridge`. See the module template for more.

- Add `ts-bridge` and `attw` as dev dependencies
- Update `build` package script to use `ts-bridge`
- Update `test` package script to run `attw --pack` after running tests

Inspect the package scripts and compare the build setup with the referenced module template. Add the requested development dependencies, update the build script to use ts-bridge, and make the test script run attw --pack after the tests. Done means the package builds in CommonJS and ESM formats and the test command completes successfully.

Written by the indexing model from the issue text.