feat(balloon): add logging for malformed balloon-stats tag

[22aronl]

Changes

Replaced Error with warn logging to the decode of BalloonStats if unknown tag is introduced. Additionally, updated integration test of BalloonStats to fail if this warn occurs.

The Result type from the update method is removed and corresponding update metrics have been removed as it is no longer tracked.

Reason

Attempting to resolve Issue 5542

License Acceptance

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• I have read and understand CONTRIBUTING.md.
• I have run tools/devtool checkbuild --all to verify that the PR passes
  build checks on all supported architectures.
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• I have described what is done in these changes, why they are needed, and
  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
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---

• This functionality cannot be added in rust-vmm.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.23%. Comparing base (d130c7d) to head (5cd0e68).
⚠️ Report is 2 commits behind head on main.

⚠️ Current head 5cd0e68 differs from pull request most recent head 7c8a9a4

Please upload reports for the commit 7c8a9a4 to get more accurate results.

Files with missing lines	Patch %	Lines
src/vmm/src/devices/virtio/balloon/device.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5572      +/-   ##
==========================================
- Coverage   83.24%   83.23%   -0.01%     
==========================================
  Files         277      277              
  Lines       29263    29265       +2     
==========================================
  Hits        24359    24359              
- Misses       4904     4906       +2     

Flag	Coverage Δ
5.10-m5n.metal	83.56% <0.00%> (-0.02%)	⬇️
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5.10-m7g.metal	80.18% <0.00%> (-0.01%)	⬇️
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6.1-m6i.metal	83.60% <0.00%> (-0.01%)	⬇️
6.1-m7a.metal-48xl	82.92% <0.00%> (-0.01%)	⬇️
6.1-m7g.metal	80.18% <0.00%> (-0.02%)	⬇️
6.1-m7i.metal-24xl	83.61% <0.00%> (-0.01%)	⬇️
6.1-m7i.metal-48xl	83.61% <0.00%> (-0.02%)	⬇️
6.1-m8g.metal-24xl	80.18% <0.00%> (-0.01%)	⬇️
6.1-m8g.metal-48xl	80.18% <0.00%> (-0.02%)	⬇️

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[JackThomson2]

Thank you for your contribution looks good. Just a couple of minor comments

[22aronl]

Thank you @JackThomson2 for the review!

I have addressed your comments. Please take another look when you have time!

[22aronl]

Thank you for the comments!

I dropped the Result type from update_with_stat. This has resulted in the removal of tracking fields of failed stats update in 2 metric files (as they are no longer being used). An alternate solution could be moving the stats_update_fails for BalloonDeviceMetrics into the update_with_stat method. Let me know if that or the current solution is fine (or another). Thanks!