Add custom span instrumentation

[djfarrelly]

Additional detail for tools.

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Summary by cubic

Add OpenTelemetry tracing around tool execution to improve observability and debugging. Each tool call now creates an "executeTool" span with useful attributes and ends cleanly on all paths.

• New Features

  • Added tracer in src/lib/traces.ts ("inngest-utah").
  • Instrumented executeTool with spans including toolCallId, name, and args.
  • Ensured spans end on success, error, and unknown tool cases.

• Dependencies

  • Added @opentelemetry/api ^1.9.0.

^{Written for commit 29691d8. Summary will update on new commits.}