Add rate limits to the token_usage event

[dgageot]

{"type":"token_usage","session_id":"823b48d7-3aa7-4ea9-8829-6f9db2930fd8","usage":{"input_tokens":13125,"output_tokens":98,"context_length":13223,"context_limit":200000,"cost":0.005421,"last_message":{"input_tokens":5,"output_tokens":98,"cached_input_tokens":13120,"cached_write_tokens":0,"limit":12000000000,"remaining":11994579000,"reset":1769442346,"Cost":0.005421,"Model":"claude-sonnet-4-20250514"}},"agent_name":"root"}