fix: Consider border size in resize observer

[jperals]

Issue #, if available:

Description of changes:

In order to calculate an element's content size from the box size, subtract not only the padding but also the border thickness, if any.

• Tested manually by adding logpoints in the container-queries dev page in the components package —for boxes with border, the measurement in the initial render was wrong by the amount of the border thickness, which gets fixed with this change
• Tested in my pipeline
• Dry run: 7532974560

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.78%. Comparing base (a5de60f) to head (fbeb392).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #165   +/-   ##
=======================================
  Coverage   98.77%   98.78%           
=======================================
  Files          36       36           
  Lines         900      904    +4     
  Branches      239      255   +16     
=======================================
+ Hits          889      893    +4     
  Misses         11       11           

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