chore(otlp): Handle partial success

[scottgerring]

Fixes #865, handling partial success for HTTP and tonic OTLP responses by logging the portion of the request that was rejected by the server and not retrying.

The relevant bit of the spec is here.

Changes

Straightforward enough! The testing is rather limited because all we're doing is parsing and logging responses; let's make sure we don't panic for invalid or empty data, as well as a minimal smoke test.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 51.31579% with 74 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.7%. Comparing base (9bbe272) to head (07670f4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-otlp/src/exporter/http/logs.rs	63.4%	15 Missing ⚠️
opentelemetry-otlp/src/exporter/http/trace.rs	63.4%	15 Missing ⚠️
opentelemetry-otlp/src/exporter/http/metrics.rs	70.2%	11 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/logs.rs	0.0%	9 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/metrics.rs	0.0%	9 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/trace.rs	0.0%	9 Missing ⚠️
opentelemetry-otlp/src/exporter/http/mod.rs	0.0%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3206     +/-   ##
=======================================
- Coverage   80.8%   80.7%   -0.2%     
=======================================
  Files        128     128             
  Lines      23090   23220    +130     
=======================================
+ Hits       18676   18754     +78     
- Misses      4414    4466     +52     

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[cijothomas]

not sure if we are actually validating anything in this test about partial-success.

[scottgerring]

@cijothomas
It's just to make sure things don't catch fire, but you are right, there is not much in the way of asserts - apart from it doesn't panic, and spans come out the end.

I changed the comment to reflect this, but if your feeling is it is overwrought it may well be and I can happily remove it. The use case here in general is straightforward enough - de-serialize and log partial success - that I don't think this adds much beyond the 'fail path' unit tests tbh.

[cijothomas]

LGTM.