Allow removing entity-less devices; evict telemetry dedup map on entity removal

[mwolter805]

Summary

Follow-up to #247 / #229. #247 made orphaned repeater/client devices removable from the HA UI and, per review, deliberately refused contact/unknown devices while the contact is still live — to avoid deleting a device while it is producing live data and leaving stale entity references behind. Two gaps remain:

1. An entity-less device is still refused while the contact is live. Once the user has already removed a device's only entity (e.g. a discovered contact's telemetry sensor), the device page shows "This device has no entities" — but Delete is still refused because the pubkey prefix is a live contact, so HA renders the rejection as an unhelpful [object Object] dialog and the empty shell can't be removed. This is the entity-less half of Remove old devices in HA #229.
2. The telemetry/GPS dedup maps are never evicted on entity removal. TelemetrySensorManager.discovered_sensors and DeviceTrackerManager.discovered_trackers cache the live entity objects by key. Nothing pops those caches when HA removes an entity (UI delete, device-delete cascade, or platform unload), so the manager keeps updating a deregistered entity and won't recreate it until an HA restart — the same desync already patched in the untracked-contact-discard (coordinator.py) and data-only-demote (services.py) flows; the UI-removal path just never reached either eviction.

Changes

• __init__.py (async_remove_config_entry_device): insert an early "device has no entities → allow removal" branch, excluding the hub (identifier == entry_id). The existing feat: allow removing orphan repeater and client devices from HA UI #247 guards (hub, subscribed repeater/client, live contact/unknown) are unchanged and still govern populated devices — the new branch is only reached when er.async_entries_for_device(..., include_disabled_entities=True) returns empty.
• telemetry_sensor.py / device_tracker.py: register async_on_remove(partial(self.discovered_*.pop, key, None)) on each telemetry sensor and GPS tracker at the manager's creation site, so removal pops the dedup key and a later telemetry/GPS event recreates the entity instead of updating a deregistered one.

Tests

• Unit (tests/test_device_removal.py): 3 added — an emptied contact device is removable even while the contact is live; the hub stays refused even when empty; a populated live contact stays refused (the feat: allow removing orphan repeater and client devices from HA UI #247 guard, preserved). Existing refusal/orphan tests run under an autouse non-empty entity-count default, so feat: allow removing orphan repeater and client devices from HA UI #247's behavior is unchanged.
• Integration (tests_integration/test_dedup_eviction.py): new regression — drives the real telemetry/GPS manager handlers under real Home Assistant, removes the entity via the entity registry, and asserts the dedup key is evicted (riding the real async_on_remove lifecycle). Fails without the eviction.
• Also verified on a live HA install: deleting an emptied contact device now succeeds with no error dialog, and no "rejected by integration" line is logged.

Compatibility / scope

• Additive — reverts nothing from feat: allow removing orphan repeater and client devices from HA UI #247. entity_registry is already imported; async_on_remove is standard HA. No dependency or version bump; the populated-device guards are preserved.
• A removed entity-less device can reappear if the node telemeters again (clean recreate, by design); permanent "ignore this contact" suppression is out of scope.

Files

• custom_components/meshcore/__init__.py — entity-less-device removal allowance (hub-excluded).
• custom_components/meshcore/telemetry_sensor.py — async_on_remove eviction of discovered_sensors.
• custom_components/meshcore/device_tracker.py — async_on_remove eviction of discovered_trackers.
• tests/test_device_removal.py — empty-device unit coverage.
• tests_integration/test_dedup_eviction.py — eviction regression (new).