feat(injector): exclude smart_icons attrs from recorder persistence

[jpettitt]

Summary

Tell HA's recorder to strip smart_icons_color and smart_icons_background from the JSON it persists to the state_attributes table. The state_changed event still fires (the painter needs it for live updates) — only the database-side payload changes:

• Stored state_attributes rows shrink (our 2 attrs gone from the JSON)
• Adjacent rows deduplicate much better, since the "real" entity attributes change less often than our decoration writes do
• No effect on RAM / in-memory event bus / frontend behaviour

Motivated by a question that came up during a separate memory-leak investigation: even though the leak turned out not to be Smart Icons, recorder-side noise reduction is a real ongoing concern for installs with broad glob rules (e.g. sensor.* mapping rules that re-evaluate on every sensor change).

This supersedes #13, which was opened against an older injector.py and conflicts after the _apply_target refactor in 0332f4a. This branch re-applies the same change cleanly onto current main, plus the API was re-verified against HA 2026.2.3 (StateInfo, State.state_info, and the state_info= kwarg on async_set all present).

Mechanism

HA's recorder reads state.state_info["unrecorded_attributes"] (a frozenset[str]) and strips matching attribute keys before writing the row. The set is per-State, populated via the optional state_info parameter to hass.states.async_set.

Two implementation points worth noting:

1. ATTR_ICON is NOT excluded. It's HA's standard glyph attribute — other integrations, templates, and user automations legitimately change it. Recording the history of icon changes is correct; only our two namespaced extensions are recorder noise.
2. The merge with existing unrecorded_attributes is load-bearing. Some integrations declare their own (e.g. a sensor that excludes last_reset from history). A naïve state_info= override would clobber the entity author's declaration. _state_info_excluding_smart_icons merges both sets.

What this is NOT

Not a memory fix. The reporter's HA install was leaking memory; investigation confirmed it's not Smart Icons (memory continued climbing with the integration uninstalled). This PR addresses a related-but-separate concern: recorder DB growth from our writes.

Test plan

• 3 new tests in tests/test_injector.py:
  • Smart-icons attrs marked unrecorded on apply
  • Entity owner's existing unrecorded_attrs preserved on merge
  • state_info still travels with release writes
• Full backend suite: 131 pass (128 previous + 3 new)
• Backend-only change — no frontend files or static/ bundles touched
• CI on this PR

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