release: 0.22.0 (root capabilities, extend, idempotent materialization)

[dcj]

Bumps __version__ to 0.22.0, promotes [Unreleased] to [0.22.0], adds the tag link. No code changes.

Issue	Change
#64	node_id callable, so one device can carry two instances of a capability
#65	DeviceTreeBuilder contract: model ownership, and the limit of add()'s ordering
#66	Data loss in 0.21.0's headline feature. The builder replaced properties in a model it does not own, discarding live values, callbacks and entity_setters. A producer that wired inbound control lost the actuator while $description kept advertising settable: true.
#67	A child could silently shadow an ancestor's or a sibling's id, putting two devices on the same topics. Plus add_root_capabilities(), the feature it was filed for.
#68	extend(), so an existing device can grow a capability. The previous workaround dropped properties from $description while leaving their retained topics on the broker.

Minor rather than patch: three new public methods. #66 is the reason not to sit on it, since 0.21.0 is live with that data loss.

Worth reading in the diff

Materialization is now idempotent at three levels: the node, the property, and the state transition itself. That last one is the substantive change. An empty state_transition() still emits init then ready, and that edge forces every controller on the bus to resync, so a re-declaration that changes nothing must not cost one. Found by a test asserting extend() publishes nothing on a re-declare, which got two publishes: the content was already idempotent, the state flap was not.

Verification

• 680 tests pass (600 at 0.20.1, 653 at 0.21.0)
• ruff check / ruff format --check clean; markdownlint clean
• python -m build produces both artifacts; wheel METADATA reads Version: 0.22.0
• Version agrees across ebus_sdk.__version__, pyproject.toml's dynamic attr, and the setup.py regex shim

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