[FEATURE] Add per-tool token cost to OpenTelemetry events

Feature Request

Claude Code's OpenTelemetry integration exports tool call events with tool name and duration, but does not include how many tokens each tool invocation costs.

Why this matters

Users can see how often each tool is called (Read, Edit, Bash, etc.) but can't determine how expensive each tool is in token terms. Without per-tool token attribution, you can't answer questions like "Read costs me 40% of my tokens" or identify which tool types drive the most spend.

Requested change

Add token count attributes (input tokens, output tokens) to tool call log events, so users can compute cost per tool type.