feat: Add support for w3c trace parent headers for outgoing requests

[markushi]

Implements #4505

Note: this isn't the same as the reverted PR below because that's about incoming requests, while this is about outgoing requests:

• Revert W3C traceparent support to tracing client and utils (#4084) #4204

[github-actions]

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[Copilot]

Pull Request Overview

This PR adds support for W3C Trace Context traceparent headers in outgoing HTTP requests to enable interoperability with OpenTelemetry-compliant distributed tracing systems.

Key Changes:

• Introduces a new W3CTraceparentHeader class that formats trace information according to the W3C Trace Context specification
• Adds a PropagateTraceparent configuration option (default: false) to control whether traceparent headers are sent
• Implements GetTraceparentHeader() method across the Hub interface hierarchy to retrieve traceparent information from active spans or propagation context

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Sentry/W3CTraceparentHeader.cs	New class implementing W3C traceparent header formatting
src/Sentry/SentryOptions.cs	Adds PropagateTraceparent configuration option
src/Sentry/SentryMessageHandler.cs	Adds logic to attach traceparent headers to outgoing HTTP requests
src/Sentry/Internal/Hub.cs	Implements GetTraceparentHeader() to construct headers from spans or propagation context
src/Sentry/IHub.cs	Adds GetTraceparentHeader() to the Hub interface
src/Sentry/SentrySdk.cs	Exposes static GetTraceparentHeader() method
src/Sentry/Extensibility/HubAdapter.cs	Forwards GetTraceparentHeader() calls to SentrySdk
src/Sentry/Extensibility/DisabledHub.cs	Returns null for GetTraceparentHeader() when hub is disabled
test/Sentry.Tests/Protocol/W3CTraceparentHeaderTests.cs	Comprehensive test coverage for W3CTraceparentHeader class
test/Sentry.Tests/HubTests.cs	Tests for Hub's GetTraceparentHeader() implementation
test/Sentry.Tests/ApiApprovalTests.Run.DotNet8_0.verified.txt	Updates API surface approval snapshot

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[bruno-garcia]

@sentry review

[codecov]

Codecov Report

❌ Patch coverage is 86.20690% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (version6@e7d6b84). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/Sentry/Extensibility/DisabledHub.cs	0.00%	1 Missing ⚠️
src/Sentry/Extensibility/HubAdapter.cs	0.00%	1 Missing ⚠️
src/Sentry/SentryMessageHandler.cs	87.50%	0 Missing and 1 partial ⚠️
src/Sentry/SentrySdk.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             version6    #4661   +/-   ##
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  Coverage            ?   73.16%           
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  Files               ?      480           
  Lines               ?    17354           
  Branches            ?     3424           
===========================================
  Hits                ?    12697           
  Misses              ?     3807           
  Partials            ?      850           

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[jamescrosswell]

We should probably document this in a more "SDK User" friendly format... I added #4663 as a follow up for this.

[jamescrosswell]

LGTM apart from the redundant = false assignment on the property, that CoPilot mentioned.

Thanks @markushi !