Standardize all energy period calculations

[karwosts]

Proposed change

We've got a couple different spots where we're trying to infer the energy period, and they sometimes have subtly different equations, so I'm not sure if it might be a bug if they come up with different result. Anyway we have a lot of magic number like "> 35" floating around and it's better to consolidate all that into a single standard function for calculating the period.

Type of change

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

Example configuration

Additional information

• This PR fixes or closes issue: fixes Energy Dashboard charts render incorrectly for date ranges spanning multiple months #28648
• This PR is related to issue or discussion:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

[karwosts]

Didn't even realize it at first but I guess this probably fixes #28648