Prepare the v0.3.0 changelog

[xhan97]

Closes the Unreleased section and dates it 2026-08-16.

Why v0.3.0

Two API changes, both breaking for older environments:

• minimum Python raised 3.9 → 3.11
• minimum numba, numpy, scikit-learn raised to 0.63.0, 2.3.2, 1.7.2

On a 0.x version, a minor bump is how that gets signalled. Last release was v0.2.4.

Changes while closing it out

Entries are reordered so the two API changes sit together near the top — that is what anyone upgrading needs to read first.

Two corrections:

• The security entry claimed "76 security advisories". That was a mid-work count taken from analysing the lockfile, not the final state. GitHub now reports every advisory resolved, so the number is dropped in favour of saying that plainly.
• A Fix entry is added for the spelling corrections in IKTOD's class docstring and the IKGOD usage example. Those are user-facing documentation and were not recorded.

Deliberately left out: the internal-only work from this batch — CI restructuring, the pre-commit repair, removal of the unused cluster/_utils.py and pixi.lock. None of it is observable to anyone installing the package.

After this merges

Tagging v0.3.0 triggers pypi.yml, which publishes to PyPI and creates a GitHub Release, and deploy-gh-pages.yml, which deploys versioned docs and moves the latest alias. A PyPI version number can never be reused, so that step should be taken deliberately rather than as a follow-on.

Verification

mkdocs build --strict passes, so the changelog page renders. All six pre-commit hooks pass.