Use floats instead of datetime in statistics

[gjohansson-ST]

Proposed change

Continuation of #110438

Reduce overhead in statistics

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: Statistics component causes significant slowdown #132597
• Link to documentation pull request:

Checklist

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[home-assistant]

Hey there @ThomDietrich, mind taking a look at this pull request as it has been labeled with an integration (statistics) you are listed as a code owner for? Thanks!

Code owner commands

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• @home-assistant unassign statistics Removes the current integration label and assignees on the pull request, add the integration domain after the command.
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[bdraco]

Fix for last_reported_timestamp with LazyState #132761