fix(metrics,logs): Don't attach span_id if no active span

[sentrivana]

Description

Per the log/metrics spec, we shouldn't attach a span ID unless there's an active span. In the current implementation, due to how the propagation context works, we'd synthesize a span ID in this case.

Circumvent that code path by directly checking for an active span.

Issues

• Closes https://linear.app/getsentry/issue/PY-2388/align-metric-span-id-attachment-with-the-metrics-spec
• Closes Align metric span_id attachment with the metrics spec #6128

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[linear-code]

PY-2388 Align metric span_id attachment with the metrics spec

[github-actions]

Codecov Results 📊

✅ 13 passed | Total: 13 | Pass Rate: 100% | Execution Time: 8.01s

All tests are passing successfully.

❌ Patch coverage is 0.00%. Project has 14873 uncovered lines.

Files with missing lines (1)

File	Patch %	Lines
scope.py	71.38%	⚠️ 251 Missing and 82 partials

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Generated by Codecov Action

[ericapisani]

Other than the notes from Cursor, this LGTM. Approving so as not to block

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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