feat(core): Rename vercelai.schema to gen_ai.request.schema

[RulaKhaled]

Renaming vercelai schema to genai schema for Vercel AI integration.

[linear]

JS-991 Emit `Schema` span property for Vercel AI

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,010	-	8,651	+4%
GET With Sentry	1,441	16%	1,353	+7%
GET With Sentry (error only)	6,404	71%	6,047	+6%
POST Baseline	1,231	-	1,171	+5%
POST With Sentry	528	43%	514	+3%
POST With Sentry (error only)	1,077	87%	1,036	+4%
MYSQL Baseline	3,377	-	3,260	+4%
MYSQL With Sentry	420	12%	452	-7%
MYSQL With Sentry (error only)	2,761	82%	2,663	+4%

View base workflow run