Seed zero-value metrics for empty buckets in count-items

[delthas]

count-items only produced metric documents for buckets that hold objects. An empty bucket yielded no document in __infostore, so Scuba's deep health check (getAnyMetric) found nothing and returned 500, causing CloudServer to disable the quota service cluster-wide (ARTESCA-17063).

This seeds zero-value entries for the empty bucket, its account and its location in getObjectMDStats() when a bucket scan yields no objects, so every known resource always has a document in __infostore.

The bucket key is derived from the __usersbucket creation date, exactly like populated buckets (S3UTILS-131), so the seeded document matches the key quota lookups use. If that date is missing, the bucket is skipped with a warning rather than written under a key that lookups could never match.

Note: this addresses only the empty-bucket case. The new-bucket window (before the first count-items run) and the Scuba deep-health-check / alert behavior are tracked separately.

Issue: S3UTILS-224

[bert-e]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.71%. Comparing base (128b8c7) to head (deb030e).
⚠️ Report is 4 commits behind head on development/1.

Additional details and impacted files

@@                Coverage Diff                @@
##           development/1     #378      +/-   ##
=================================================
+ Coverage          45.47%   45.71%   +0.24%     
=================================================
  Files                 88       88              
  Lines               6529     6549      +20     
  Branches            1372     1377       +5     
=================================================
+ Hits                2969     2994      +25     
+ Misses              3510     3505       -5     
  Partials              50       50              

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[claude]

LGTM

Review by Claude Code

[benzekrimaha]

LGTM

[delthas]

/approve

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[bert-e]

I have successfully merged the changeset of this pull request
into targetted development branches:

• ✔️ development/1

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• development/1.13
• development/1.14
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• development/1.16
• development/1.17
• development/1.18
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• development/1.7

Please check the status of the associated issue S3UTILS-224.

Goodbye delthas.