Instrument Cloudflare Clairic as gen_ai.extract spans #25615

The Extraction span spec adds gen_ai.extract spans. The JS SDK does not emit them.

Current behavior

getOperationName in packages/server-utils/src/ai/workers-ai/utils.ts sends only typesafe/jev and @cf/cloudflare/clef to decide. A Clairic call ({state, fields}, no messages / prompt / text) falls through to chat. The result is a chat @cf/cloudflare/clairic span with no input or output messages.

To do

• Bump @sentry/conventions when it has GEN_AI_EXTRACT (it is not in the package yet).
• Send @cf/cloudflare/clairic to an extract operation: op gen_ai.extract, name extract {model}, gen_ai.operation.name: "extract".
• gen_ai.input.messages: the request body as the caller passed it, without model. Replace each image with "[Blob substitute]".
• gen_ai.output.messages: the response body as the provider returned it, without model and usage. Keep truncated.
• Set gen_ai.usage.input_tokens / output_tokens. Do not send the other Clairic usage counts (state_tokens, image_tokens, schema_tokens, passes).
• Add an integration test, and add an extract call to the Workers AI e2e app.