fix: handle HTTP 413 by splitting and retrying in OTLP HTTP exporters

[Krishnachaitanyakc]

Summary

When a backend returns HTTP 413 (Payload Too Large), the OTLP HTTP trace and log exporters now split the batch in half and recursively retry each half, preventing silent data loss when batch sizes exceed backend limits.

Fixes #4533

Changes

• Added _is_payload_too_large() helper in _common/__init__.py
• Refactored export() to delegate to _export_batch() in both trace and log exporters
• _export_batch() handles 413 responses with binary splitting:
  • Base case: single-item batch returns FAILURE (item is genuinely too large)
  • Deadline guard: if deadline expired, returns FAILURE without recursing
  • Short-circuit: if first half fails, second half is not attempted
  • Recursive split: halves the batch and exports each half independently

Notes

• The metric exporter already has proactive batch splitting via max_export_batch_size and _split_metrics_data(). Reactive 413 handling for metrics is deferred to a follow-up since metric data has a nested protobuf structure that requires different splitting logic.
• The gRPC exporter uses a different status code system (RESOURCE_EXHAUSTED) and would need separate handling in a future PR.

Test plan

• 5 new span exporter tests: split success, single-item failure, recursive splitting, partial failure short-circuit, deadline expiry
• 5 new log exporter tests: same scenarios
• All existing tests pass (no regressions)
• ruff linter passes

[DylanRussell]

Do other languge's OTLP HTTP exporters do something similar ? It'd be good to see how other languages handle this..

[Krishnachaitanyakc]

I checked on this to see how other OTel language SDKs handle HTTP 413:

OTLP Specification (otlp/#failures): Only 429, 502, 503, and 504 are listed as retryable. 413 is not mentioned at all, and the spec says "All other 4xx or 5xx response status codes MUST NOT be retried."

SDK	413 Handling	Batch Splitting
Go (client.go)	Non-retryable, immediate failure	No
Java (HttpExporter.java)	Non-retryable, immediate failure. Has open issue #5394 for oversized payloads.	No
.NET	Non-retryable	No
JavaScript	Non-retryable	No

No other SDK currently handles 413 with batch splitting. This PR would make Python the first to implement this recovery strategy.

Also, the spec says 4xx codes "MUST NOT be retried" but splitting and retrying with a smaller payload is not the same as retrying the same request. It's a distinct recovery strategy. The current behavior in all SDKs is silently dropping the entire batch, which causes data loss.

[tammy-baylis-swi]

Thank you for starting this @Krishnachaitanyakc , and for checking the spec and other instrumentors.

The scope of #4533 is vague, especially given the current state of OTel Python's OTLP HTTP vs gRPC, span/metrics/logs export. I'm going to comment there.