chore: OTLP retry post-review cleanup

[scottgerring]

Fixes #
Follow on from #3126

Changes

Please provide a brief description of the changes here.

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 62.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.7%. Comparing base (3b2f751) to head (e7c40bd).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-otlp/src/retry.rs	62.5%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3204     +/-   ##
=======================================
- Coverage   80.8%   80.7%   -0.2%     
=======================================
  Files        128     128             
  Lines      23090   23247    +157     
=======================================
+ Hits       18676   18772     +96     
- Misses      4414    4475     +61     

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[scottgerring]

Open for suggestions for where we can put the runtime selection. This strikes me as a broader question about the stabilisation of the runtime mechanism.

https://github.com/scottgerring/opentelemetry-rust/blob/9ba3a06df952d4888009764bebe665281f9e45b7/opentelemetry-otlp/src/exporter/http/mod.rs#L402-L409

[cijothomas]

otel_warn!(
                            name: "Export.Failed.NonRetryable",
                            operation = operation_name,
                            message = "OTLP export failed with non-retryable error - telemetry data will be lost"
                        );

[scottgerring]

Should be good; removed the error inline from each of these.

[cijothomas]

otel_warn!(
name: "Export.Retry.Exhausted",
operation = operation_name,
retries = attempt,
message = "OTLP export failed after all retry attempts - telemetry data will be lost"
);

[scottgerring]

@cijothomas the build failure split out here has nothing to do with this change:
#3216