fix(streaming): Set segment source if unset

[sentrivana]

Description

Set segment source if not set.

Also, add streaming versions of tests in tracing/test_integration_tests.py.

Issues

Part of #5395

Reminders

• Please add tests to validate your changes, and lint your code using uv run ruff.
• 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

[sentry-warden]

Streaming span payload accessed with wrong key "transaction" instead of attributes["sentry.segment.name"]

In test_continue_trace_span_streaming, the falsy-branch asserts trace1_payload["transaction"] == "hi", but streaming span envelopes use the _to_json() format which has "name", not "transaction". The else-branch of the same test correctly uses trace1_payload["attributes"]["sentry.segment.name"], making the falsy-branch a copy-paste error that will raise KeyError at runtime.

Evidence

• StreamedSpan._to_json() (traces.py:592) produces a dict with keys "name", "trace_id", "attributes", etc., but no top-level "transaction" key.
• test_continue_trace_span_streaming uses capture_envelopes, so trace1.items[0].payload.json is the raw _to_json() output.
• The else-branch of the same test correctly accesses trace1_payload["attributes"]["sentry.segment.name"], confirming the expected format.
• The non-streaming counterpart test_continue_trace calls trace1.get_transaction_event() which does return a "transaction" key — this is the source of the copy-paste.

_{Identified by Warden code-review}

[github-actions]

Codecov Results 📊

✅ 96032 passed | ❌ 1 failed | ⏭️ 6328 skipped | Total: 102361 | Pass Rate: 93.82% | Execution Time: 335m 28s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +91
Passed Tests	📈 +102
Failed Tests	📈 +1
Skipped Tests	📉 -12

➕ New Tests (1)

View new tests

• test_profile_captured
  • File: tests.profiler.test_transaction_profiler
  • Status: ❌ Failing

❌ Failed Tests

test_profile_captured

File: tests.profiler.test_transaction_profiler
Suite: py3.8-common
Error: tests/profiler/test_transaction_profiler.py:290: in test_profile_captured assert len(items["profile"]) == 1 E assert 0 == 1 E + where 0 = len([])

Stack Trace

tests/profiler/test_transaction_profiler.py:290: in test_profile_captured
    assert len(items["profile"]) == 1
E   assert 0 == 1
E    +  where 0 = len([])

✅ Patch coverage is 100.00%. Project has 2511 uncovered lines.

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