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 80.8%. Comparing base (796ac1a) to head (c27ef5e).
⚠️ Report is 1 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%   80.8%   -0.1%     
=======================================
  Files        129     129             
  Lines      23199   23203      +4     
=======================================
+ Hits       18749   18750      +1     
- Misses      4450    4453      +3     

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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

[scottgerring]

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

[cijothomas]

LGTM- left a comment on lowering severity for retry attempts.

[scottgerring]

@cijothomas pushed log level change