[OTLP] Avoid redundant allocations and log HTTP export success

[martincostello]

Changes

Found while working on #6463.

• Avoid Uri.ToString() allocations when logging in OTLP export clients if the event source is not enabled at the relevant logging levels.
• Log successful HTTP export for parity with gRPC.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[Copilot]

Pull Request Overview

This PR optimizes OTLP export clients by avoiding redundant string allocations in logging and adds parity between HTTP and gRPC export clients by logging successful HTTP exports.

• Avoids Uri.ToString() allocations when event source is not enabled at the relevant logging levels
• Adds success logging for HTTP export to match existing gRPC behavior
• Introduces helper methods with logging level checks to prevent unnecessary allocations

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
OpenTelemetryProtocolExporterEventSource.cs	Added helper methods with event level checks to avoid Uri.ToString() allocations
OtlpHttpExportClient.cs	Added success logging for HTTP export completion
OtlpGrpcExportClient.cs	Updated to use new helper methods that avoid string allocations
CHANGELOG.md	Updated to document performance improvements and feature parity

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[codecov]

Codecov Report

❌ Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.62%. Comparing base (5f66728) to head (64181d8).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...tation/OpenTelemetryProtocolExporterEventSource.cs	50.00%	3 Missing ⚠️
...mplementation/ExportClient/OtlpGrpcExportClient.cs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6562      +/-   ##
==========================================
- Coverage   86.63%   86.62%   -0.01%     
==========================================
  Files         258      258              
  Lines       11888    11895       +7     
==========================================
+ Hits        10299    10304       +5     
- Misses       1589     1591       +2     

Flag	Coverage Δ
unittests-Project-Experimental	86.61% <55.55%> (+0.27%)	⬆️
unittests-Project-Stable	86.60% <44.44%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...mplementation/ExportClient/OtlpHttpExportClient.cs	100.00% <100.00%> (ø)
...mplementation/ExportClient/OtlpGrpcExportClient.cs	75.28% <50.00%> (ø)
...tation/OpenTelemetryProtocolExporterEventSource.cs	84.52% <50.00%> (-2.66%)	⬇️

... and 1 file with indirect coverage changes

[rajkumar-rangaraj]

No need to update changelog for this change as it is related to internal logging.

[rajkumar-rangaraj]

left a comment to remove updates to changelog

[rajkumar-rangaraj]

We don't need to include this update in the changelog, as it doesn't have any relevance for the customer.

[martincostello]

Is there no way for users to enable it by listening the event source themselves if they want to debug?

[rajkumar-rangaraj]

Including these kinds of updates in the changelog could quickly become too noisy. Since this isn’t something most customers will act on directly, I’d lean toward leaving it out and this is what earlier maintainers too followed as guidelines in this repo.