#2 Add safe span attribute helper

Summary

• add setSpanAttributesSafe for filtering and setting valid OpenTelemetry span attributes
• export the helper from the package entry point
• add coverage for supported scalar/array values and dropped invalid values

Validation

• git diff --check
• Unable to run pnpm test, pnpm typecheck, or pnpm build because pnpm and installed dependencies are unavailable in the sandbox.

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Summary by cubic

Adds setSpanAttributesSafe, a helper that only sets valid OpenTelemetry span attributes and returns the count of attributes set. Valid values are strings, numbers, booleans, and homogeneous arrays of those; empty keys and anything else are dropped. Exports the helper from the package entry point and adds tests covering valid and invalid values.