Fix listener callback contracts across domain APIs (#72)

[Faerkeren]

Issue validity assessment

Closes #72.

Verified valid and reproducible by reading the source:

• Entity._schedule_value (src/haclient/entity/base.py:175-189) dispatches every granular listener with two positional arguments (old, new).
• Several public on_* listener decorators across domain modules documented a zero-argument or single-value callback. A user following those docs would register a callable that raises TypeError when the event fires; the exception is caught and logged by _schedule_value, so from the caller's perspective the listener silently does nothing.
• Every on_* method also used func: Any) -> Any, so mypy could not catch the mismatch at the boundary.

The runtime behaviour is already what the (small majority of) docs and every existing test expect, so the issue's recommended path — keep (old, new) and align docs + types with it — is correct.

Fix

Smallest correct change:

• Standardise every domain listener docstring on the (old, new) contract: light, switch, binary_sensor, sensor, cover, lock, climate, humidifier, media_player, timer, vacuum, valve, scene, air_quality, fan.
• Replace func: Any) -> Any with func: ValueChangeHandler) -> ValueChangeHandler on every public on_* method. ValueChangeHandler is Callable[[Any, Any], Any] defined in haclient.entity.base, so existing internal storage (list[ValueChangeHandler]) needed no change.
• Drop now-unused typing.Any imports.

Timer's event-driven on_finished / on_cancelled listeners also receive two positional arguments ((entity_id, event_data)), which is structurally identical to ValueChangeHandler, so they get the same typed signature.

The event domain's on_event(self, func: Callable[[str], Any]) is a different, already-typed contract and was intentionally not touched.

Tests / checks

tests/test_granular_events.py already pins the (old, new) shape across every domain. Six new regression tests were added at the bottom:

• test_state_transition_callback_receives_old_and_new — pins the transition-listener contract.
• test_attr_change_callback_receives_old_and_new — pins the attribute-listener contract.
• test_state_value_callback_receives_old_and_new — pins the state-value-listener contract.
• test_zero_argument_callback_is_logged_and_skipped — verifies that a misused zero-argument callback raises TypeError, gets logged at ERROR, and does not break other handlers registered for the same event.
• test_media_change_callback_receives_old_and_new — pins the MediaPlayer.on_media_change (NowPlaying, NowPlaying) contract.
• test_timer_event_callback_receives_entity_id_and_data — pins the timer event-listener (entity_id, data) contract.

Validation run on this branch:

• ruff check src tests — pass
• ruff format --check src tests — pass
• mypy src (strict) — Success: no issues found in 37 source files
• pytest tests/ --cov=haclient --cov-fail-under=95 — 291 passed, total coverage 97.07%