feat(fastrace-opentelemetry): add bridge for current local context

[andylokandy]

Closes #141

[Copilot]

Pull request overview

This PR adds a bridge function to convert fastrace's thread-local parent context into an OpenTelemetry SpanContext, enabling interoperability with OpenTelemetry-based instrumentation. It also includes minor refactoring of variable names in the global collector for improved clarity.

Key changes:

• Introduces current_opentelemetry_context() function to extract the current fastrace local parent as an OpenTelemetry span context
• Refactors variable naming in global_collector.rs to reduce verbosity and improve scoping
• Updates documentation with examples demonstrating the new bridging functionality

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
fastrace/src/collector/global_collector.rs	Refactored variable names from global_collector to collector for brevity and introduced scoped blocks to improve lock lifecycle management
fastrace-opentelemetry/src/lib.rs	Added current_opentelemetry_context() function and renamed SpanContext import to OtelSpanContext to avoid naming conflicts
fastrace-opentelemetry/tests/context.rs	Added integration test verifying that OpenTelemetry spans can be correctly parented by fastrace local parent spans
fastrace-opentelemetry/README.md	Added new documentation section explaining how to activate OpenTelemetry trace context, fixed typo in "otlp", and updated dependency versions
fastrace-opentelemetry/Cargo.toml	Added enable feature to fastrace dev-dependency for testing
fastrace-opentelemetry/CHANGELOG.md	Added entry documenting the new helper functionality

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