Updated release notes for 2.16.0

[rabernat]

This PR prepares our release notes for the 2.16.0 release. I'll do the release as soon as this is merged.

TODO:

• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[rabernat]

Codecov upload failed again:

[2023-07-19T13:32:37.869Z] ['info'] Pinging Codecov: https://codecov.io/upload/v4?package=github-action-3.1.4-uploader-0.6.1&token=*******&branch=docs%2Fprep-2.16.0-release&build=5599658677&build_url=https%3A%2F%2Fgithub.com%2Fzarr-developers%2Fzarr-python%2Factions%2Fruns%2F5599658677&commit=022a216cfdf6b36d4967e3953414aa27860c0c22&job=Linux+Testing&pr=1471&service=github-actions&slug=zarr-developers%2Fzarr-python&name=&tag=&flags=&parent=
[2023-07-19T13:32:37.869Z] ['verbose'] Passed token was 0 characters long
[2023-07-19T13:32:37.869Z] ['verbose'] https://codecov.io/upload/v4?package=github-action-3.1.4-uploader-0.6.1&branch=docs%2Fprep-2.16.0-release&build=5599658677&build_url=https%3A%2F%2Fgithub.com%2Fzarr-developers%2Fzarr-python%2Factions%2Fruns%2F5599658677&commit=022a216cfdf6b36d4967e3953414aa27860c0c22&job=Linux+Testing&pr=1471&service=github-actions&slug=zarr-developers%2Fzarr-python&name=&tag=&flags=&parent=
        Content-Type: 'text/plain'
        Content-Encoding: 'gzip'
        X-Reduced-Redundancy: 'false'
[2023-07-19T13:32:38.087Z] ['error'] There was an error running the uploader: Error uploading to [https://codecov.io:](https://codecov.io/) Error: There was an error fetching the storage URL during POST: 404 - {'detail': ErrorDetail(string='Unable to locate build via Github Actions API. Please upload with the Codecov repository upload token to resolve issue.', code='not_found')}
[2023-07-19T13:32:38.088Z] ['verbose'] The error stack is: Error: Error uploading to [https://codecov.io:](https://codecov.io/) Error: There was an error fetching the storage URL during POST: 404 - {'detail': ErrorDetail(string='Unable to locate build via Github Actions API. Please upload with the Codecov repository upload token to resolve issue.', code='not_found')}
    at main (/snapshot/repo/dist/src/index.js)

This was the same issue seen in #1459 (comment). @d-v-b how did you manage to resolve that?

[d-v-b]

@rabernat I just clicked on the checks tab at the top of the PR, then hit the rerun all jobs button on the far right of the page. I'm sure there's a better way to do this with the github cli...

[rabernat]

I propose that we merge this without the codecov report, since it doesn't include any actual code changes. (Codecov issue is tracked in #1472.)

[joshmoore]

👏