ref: Per-bucket limits, fix envelope chunking (8)

[sentrivana]

Description

• correctly splice spans into multiple envelopes if a bucket contains more than 1000 spans from the same trace_id
• add weight-based flushing (actual limit is 10 MB, we flush at 5 MB)
• apply the weight and amount limits per trace_id rather than globally
• add trace_id, parent_span_id to the transport format

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 📊

✅ 1772 passed | ⏭️ 166 skipped | Total: 1938 | Pass Rate: 91.43% | Execution Time: 3m 24s

All tests are passing successfully.

❌ Patch coverage is 22.73%. Project has 11813 uncovered lines.

Files with missing lines (1)

File	Patch %	Lines
_span_batcher.py	32.86%	⚠️ 47 Missing

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