Fix Shelly EM/3EM invalid energy value after reboot

[thecode]

Proposed change

Fix invalid Shelly EM/3EM energy value after reboot:
Latest Shelly firmware sends -1 after reboot which makes a jump in the energy value, according to Shelly API -1 is valid to indicate the value is not available. This PR fixes it. I noticed other sensors may need this fix, but for now as a bugfix I keep this only to the relevant sensors .

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)
• 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 Incorrect values in energy consumption with Shelly 3EM  #67746, fixes Corrupted data in Energy monitor after Shelly 3EM rebooted #66725
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
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• Tests have been added to verify that the new code works.

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[probot-home-assistant]

Hey there @balloob, @bieniu, @chemelli74, mind taking a look at this pull request as it has been labeled with an integration (shelly) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[chemelli74]

LGTM