feat!: publish as esm-only

[achingbrain]

Following on from the conversation in https://github.com/ipld/ipld/issues/224 this converts this repo to use the latest aegir with Unified CI.

1. Remove all build related dev deps apart from aegir
2. Run the npx aegir check-project command to update project config
3. Remove non-Unified-CI github actions
4. Update imports to import from src/index.js instead of @ipld/dag-pb
5. Rename test/*.js to test/*.spec.js so aegir can find them
6. Update tsconfig.json to extend config from aegir
7. Remove "main" and other unused fields from package.json
8. Use chai from aegir pre-configured with plugins we use
9. Fixes everything the linter complains about

This will need a follow up PR to protocol/.github to add this repo to the Unified CI config file so it'll get automated config updates in the future.

Apologies that this PR is so noisy, most of it is from the check-project command

[achingbrain]

To roll the multiformats upgrade in here this will need:

• [x] https://github.com/multiformats/js-multiformats/issues/213
• [x] https://github.com/multiformats/js-multiformats/pull/217

[github-actions[bot]]

:tada: This PR is included in version 8.0.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: