hotfix: proper error handling in plausible provider

[limwa]

This PR adds proper error handling code to PlausibleProvider to protect from situations where devices don't implement battery save mode capabilities. If a device doesn't implement them, we consider that the device never is in battery saving mode.

Review checklist

• Terms and conditions reflect the current change
• Contains enough appropriate tests
• If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• Properly adds an entry in changelog.md with the change
• If PR includes UI updates/additions, its description has screenshots
• Behavior is as expected
• Clean, well-structured code

[codecov]

Codecov Report

Merging #1185 (1cc7990) into master (e2e949f) will decrease coverage by 0%.
Report is 1 commits behind head on master.
The diff coverage is 0%.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1185   +/-   ##
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- Coverage      16%     16%   -0%     
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  Files         229     229           
  Lines        6951    6958    +7     
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  Hits         1086    1086           
- Misses       5865    5872    +7