fix: structured stacktrace capture in Ruby observability plugin

[ccschmitz-launchdarkly]

Summary

Improve the Ruby observability plugin in two areas:

• Structured stacktraces on exceptions: Both the Rack Middleware and the Rails record_launchdarkly_exception helper now attach an exception.structured_stacktrace JSON attribute (via SourceContext.build_structured_stacktrace) when recording exceptions on spans. This enables richer error display in the observability UI.
• Standalone logger for non-Rails apps: New LaunchDarklyObservability.logger module method returns an OtelLogBridge that writes to both a local IO (e.g. $stdout) and the OTel Logs pipeline with trace/span correlation. Falls back to a plain Logger if the OTel logger provider isn't available yet. The OtelLogBridge now accepts an optional io: parameter and propagates level/formatter changes to the local logger.

The Sinatra demo app is updated to use the new logger, and the demo Gemfile.lock picks up the OpenTelemetry log exporter/SDK dependencies.

How did you test this change?

• Added unit tests for LaunchDarklyObservability.logger covering OTel bridge return, plain Logger fallback, and IO output verification (module_methods_test.rb)
• Added unit tests for OtelLogBridge dual-output mode covering IO + OTel emission, OTel-only mode, level propagation, and hash message handling (otel_log_bridge_test.rb)

Are there any deployment considerations?

None. These are additive changes to the Ruby gem with no breaking API changes.

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Note

Low Risk
Low risk: changes are additive and primarily enrich telemetry (extra exception attributes and optional dual-output logging) without altering core SDK behavior or request handling flow.

Overview
Adds a new LaunchDarklyObservability.logger helper for non-Rails apps that returns an OtelLogBridge capable of writing to a local IO (e.g. $stdout) and exporting OTLP log records with trace/span correlation, falling back to a plain Logger if the OTel logger provider isn’t ready.

Improves exception telemetry by consistently attaching a JSON exception.structured_stacktrace attribute when recording exceptions (module record_exception, Rack Middleware, and Rails record_launchdarkly_exception) via a new SourceContext.exception_attributes helper, and expands tests/docs/demo app accordingly (including adding OTLP logs dependencies in the Sinatra demo lockfile).

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[SpennyNDaJets]

Code makes sense to me!

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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