fix(tracing): Restore scope transaction after streamed segment ends

[kcons]

Streamed root segments wrote their name and source to the scope but never restored them on end, so later error events picked up a stale transaction. Save and restore both, and drop an inherited source when a no-op segment starts without one.

#7774 was closed on the basis that span streaming avoids this, but the same leak exists in streamed_span. This fix snapshots and restores state per root segment, so ending a child span doesn't clear the transaction (the concern raised on #7773).

Refs #7774

[github-actions]

Coverage Results 📊

✅ 133768 passed | ⏭️ 7276 skipped | Total: 141044 | Pass Rate: 94.84% | Execution Time: 478m 33s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +102
Passed Tests	📈 +102
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

✅ Patch coverage is 94.44% (17 of 18 changed executable lines covered; target 80%).
Project statement coverage is 90.24% (down 0.02 percentage points from base (0f7acd5) to head (069518d)).

Changed files with executable lines (2)

File	Patch coverage	Changed executable lines
sentry_sdk/traces.py	100.00%	16/16 covered; partial branches: 708, 737
sentry_sdk/scope.py	50.00%	1/2 covered; missed: 937

Coverage diff

@@            Coverage Diff             @@
##        master     #8049       +/-##
==========================================
- Coverage    90.26%    90.24%    -0.02%
==========================================
  Files          202       202         —
  Tracked lines     26660     26678       +18
  Branches      9926      9934        +8
==========================================
+ Hits         24062     24073       +11
- Misses        2598      2605        +7
- Partials      1510      1511        +1

---

Generated by Coverage Action