feat: Add SDK wrapper metric tagging

[tarqd]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Provide links to any issues in this repository or elsewhere relating to this pull request.

Describe the solution you've provided

Add a tag named sdkWrapper populated by the x-launchdarkly-wrapper header when provided

Describe alternatives you've considered

Provide a clear and concise description of any alternative solutions or features you've considered.

Additional context

Tagging metrics by wrapper name/version requested by customer

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Note

Adds sdkWrapper metric tag (from X-LaunchDarkly-Wrapper) across measures, middleware, and events exporter, and changes empty tag sanitization to not-provided.

• Metrics:
  • Add sdkWrapper tag key and include in publicTags/privateTags in internal/metrics/constants.go.
  • Extend WithGauge, WithCount, and WithRouteCount to accept sdkWrapper and tag it.
  • Update sanitizeTagValue to return "not-provided" for empty/whitespace and replace / with _.
  • Events exporter: parse sdkWrapper tag, include it in connection keys, and emit it in connections, newConnections, and pollingCounts payloads.
• Middleware:
  • Read X-LaunchDarkly-Wrapper via getSDKWrapper and pass to metrics helpers in connection/request counters.
• Tests:
  • Update metrics and middleware tests to expect sdkWrapper tag (defaulting to "not-provided") and new sanitization behavior; add tests for getSDKWrapper.

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