Avoid reschedule churn in Storage.async_delay_save (#111091)

* Avoid circular import in Storage.async_delay_save

We call Storage.async_delay_save for every entity being added or removed
from the registry. The late import took more time than everything else
in the function.

* Avoid reschedule churn in Storage.async_delay_save

When we are adding or removing entities we will call async_delay_save
quite often which has to add and remove a TimerHandle on the event loop
which can add up when there are a lot of registry items changing.

If the timer handle still has 80% of the time remaining on it
we will avoid resceduling and let it fire at the time the
original async_delay_save call was made. This ensures we
do not force the event loop to rebuild its heapq because
too many timer handlers were cancelled at once

* div0

* add coverage for 0 since we had none

* fix bad conflict

* tweaks

* tweaks

* tweaks

* tweaks

* tweaks

* tweaks

* more test fixes

* mqtt tests rely on event loop overhead

tests/components/frontend/test_init.py

@@ -1,10 +1,10 @@
 """The tests for Home Assistant frontend."""
-from datetime import timedelta
 from http import HTTPStatus
 import re
 from typing import Any
 from unittest.mock import patch
 
+from freezegun.api import FrozenDateTimeFactory
 import pytest
 
 from homeassistant.components.frontend import (
@@ -20,7 +20,6 @@ from homeassistant.components.websocket_api.const import TYPE_RESULT
 from homeassistant.core import HomeAssistant
 from homeassistant.loader import async_get_integration
 from homeassistant.setup import async_setup_component
-from homeassistant.util import dt as dt_util
 
 from tests.common import MockUser, async_capture_events, async_fire_time_changed
 from tests.typing import MockHAClientWebSocket, WebSocketGenerator
@@ -220,7 +219,10 @@ async def test_themes_persist(
 
 
 async def test_themes_save_storage(
-    hass: HomeAssistant, hass_storage: dict[str, Any], frontend_themes
+    hass: HomeAssistant,
+    hass_storage: dict[str, Any],
+    freezer: FrozenDateTimeFactory,
+    frontend_themes,
 ) -> None:
     """Test that theme settings are restores after restart."""
 
@@ -233,7 +235,8 @@ async def test_themes_save_storage(
     )
 
     # To trigger the call_later
-    async_fire_time_changed(hass, dt_util.utcnow() + timedelta(seconds=60))
+    freezer.tick(60.0)
+    async_fire_time_changed(hass)
     # To execute the save
     await hass.async_block_till_done()