Refactor entity_platform polling to avoid double time fetch

[bdraco]

Proposed change

Replace async_track_time_interval with loop.call_later to avoid the useless time fetch and datetime object construction every time the listener fired since we always throw it away. Fetching time is a lot more expensive on some aarch64 system (ie Home Assistant Blue) because they cannot use VDSO due to arm errata.

In most cases, this is the second most frequent call listener after the update coordinator which already uses a similar scheduling design to avoid this problem.

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• This PR fixes or closes issue: fixes #
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