Release Zarr-Python v3.3.0

[maxrjones]

Release: v3.3.0
Scheduled Date: 2026/07/16

Before release:

• Check SPEC 0 to see if the minimum supported version of Python or NumPy needs bumping.
• Verify that the latest CI workflows on main are passing: Tests, GPU Tests, Hypothesis, Docs, Lint, Wheels.
• Run the downstream tests against main: go to the workflow page, click "Run workflow", and select the main branch. Verify that the Xarray and numcodecs integration tests pass.
• Open a release PR with the changelog entries for the upcoming release, generated with uv run --only-group release towncrier build --version x.y.z.
• Review the release PR and verify the changelog in docs/release-notes.md looks correct.
• Merge the release PR.

Release:

• Draft a new GitHub Release with tag vX.Y.Z targeting main. Use "Generate release notes" for the description.
• Verify the release is published on PyPI and ReadTheDocs.

After release:

• Review and merge the pull request on the conda-forge zarr-feedstock that will be automatically generated.

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• Party 🎉

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Releasing from a branch other than main

In rare cases (e.g. patch releases for an older minor version), you may need to release from a dedicated release branch (e.g. 3.1.x):

• Create the release branch from the appropriate tag if it doesn't already exist.
• Cherry-pick or backport the necessary commits onto the branch.
• Run towncrier build --version x.y.z and open the release PR against the release branch instead of main.
• Run the downstream tests against the release branch instead of main.
• When drafting the GitHub Release, set the target to the release branch instead of main.
• After the release, ensure any relevant changelog updates are also reflected on main.