ref: Add experimental streaming API (5)

[sentrivana]

Description

Add sentry_sdk.traces.start_span and the corresponding scope method.

NOTE: This is experimental and not production ready code.

Issues

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

[github-actions]

Codecov Results 📊

✅ 14 passed | Total: 14 | Pass Rate: 100% | Execution Time: 3.06s

All tests are passing successfully.

❌ Patch coverage is 33.33%. Project has 14928 uncovered lines.

Files with missing lines (2)

File	Patch %	Lines
scope.py	63.27%	⚠️ 306 Missing and 73 partials
traces.py	53.97%	⚠️ 58 Missing

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Generated by Codecov Action

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

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