prepare pypi metadata, credit hydra, link docs

[vgreg]

Prepares the package for its first PyPI release and adds attribution to Hydra.

Packaging metadata

• Add authors, [project.urls] (Homepage, Documentation, Repository, Issues, Changelog), keywords, and classifiers. The PyPI page previously had no author and no sidebar links.
• Switch license = { text = "MIT" } to the PEP 639 SPDX form license = "MIT" plus license-files = ["LICENSE"]. The metadata now carries License-Expression: MIT, so the deprecated License :: OSI Approved :: MIT License classifier is deliberately omitted (PyPI rejects packages that declare both).
• Development Status :: 3 - Alpha, matching the not-yet-stable warning in the README.

Version drift fix

bump-my-version only rewrote pyproject.toml, so iolaus.__version__ would have stayed at 0.1.0 forever. Added a second [[tool.bumpversion.files]] entry for src/iolaus/__init__.py.

Housekeeping

• .DS_Store added to .gitignore and removed from the working tree.
• CHANGELOG.md gets a real 0.1.0 section (contents checked against the actual implementation) with Keep a Changelog formatting and compare links.

Documentation

• README links to https://www.vincentgregoire.com/iolaus/, and mkdocs.yml gains the matching site_url.
• New "Relationship to Hydra" section in both the README and the docs home page, crediting Hydra for the inspiration and stating plainly that Iolaus implements only the subset of its features in day-to-day use. The docs version includes a feature comparison table pointing readers to Hydra when they need config groups, multirun sweeps, structured configs, object instantiation, or launcher plugins.

Verification

• uv build + twine check pass on both sdist and wheel
• 15 tests pass, ruff check and mypy --strict clean
• mkdocs build --strict clean, comparison table renders
• bump-my-version bump --dry-run patch confirmed to touch both version locations

Trusted Publishing on PyPI is still to be configured, and is not part of this PR.

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