Release: 0.3.0

• Breaking: cluster + other and assembler + other now return a new instance and leave both operands unchanged. Use += to add other in place (the old behavior of "+").
• Breaking: Assembler now validates every constructor added with insert, append, extend, prepend, or item assignment, and raises a TypeError for anything that is not a wonka-compatible constructor. Before, only add validated.
• Added the py.typed marker so that type checkers use the type hints in wonka.
• Added a subset method to Manufacturer.
• Added slice support to Assembler indexing, assignment, and deletion.
• Added the Parameters type alias for the parameters argument (a mapping with str keys).
• Fixed Assembler.prepend, which added the contents of an Assembler instead of the Assembler itself.
• Fixed Registrar.create, which did not accept the keyword arguments that every Factory.create accepts.
• Fixed Subclasser choosing between subclasses with the same name in a random order. Subclasses are now found in a fixed, depth-first order without duplicates.
• Fixed the undefined names in the Sourcerer recipe.
• Removed the unfinished and broken Hub and Keystone classes, which were not exported or documented.
• Removed the unused _is_sequence and _return_subset utilities, the duplicate _iterify, the unused GenericList, GenericSet, and SubsetReturns aliases, and the commented-out code.
• Updated to the snickerdoodle 0.5.0 template (Codecov coverage, a coverage page in the docs, pydoclint, Python 3.15, SPDX license metadata, a version read from __version__, GitHub CLI releases, and uv updates from Dependabot). Added .cruft.json so that cruft update can apply future template changes.
• Removed the leftovers from pdm (the credits page and the script that read pdm.lock) and moved the issue templates out of a nested ISSUE_TEMPLATE folder.
• Restyled the package (spaces around keyword argument =, closing brackets on the last line, section markers, and complete docstrings). Ruff now enforces single quotes and the 80 character line limit, and ignores the tests folder when run by pre-commit.
• mypy now passes (there were 39 errors) and runs in CI.
• Reorganized the tests by module, added a fixture that restores the global options after each test, and added tests for the operators, slices, validation, subset, the dispatchers, the options, and the package metadata (100 tests in total, with 99% coverage).