fix(overview_metrics): opt-in strict counts (ISSUE-123)

[dwolfson]

Summary

count_elements and its siblings turn a failed query into 0, so an outage or auth failure looks like an empty catalog (ISSUE-123). This adds an opt-in strict flag and leaves the default alone.

• strict=False (default): unchanged, a failure counts as 0.
• strict=True: returns None when the count is not known:
  • the fallback find_metadata_elements query raised;
  • it returned something that is neither a list nor pyegeria's miss string;
  • it returned a full page (DEFAULT_CAP), which is only a lower bound.
• A native count is trusted as is, even above the cap. A real zero (an empty list, or "No elements found") is still 0.
• Each None logs a warning that says why.
• Covers count_elements, count_elements_by_property, counts_by_type, people_counts and usage_context_counts.
• strict is declared on those five analytic-registry entries, so a report spec can pass it.
• PYEGERIA_ISSUES.md: ISSUE-123 is moved to Fixed.

Closes #424

Test plan

• New tests/micro-tests/test_issue_123_strict_counts.py
• pytest tests/micro-tests: 1085 passed, 1 skipped

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