feat(nextjs): Set cloudflare runtime

[chargome]

We want to gain better insights how much usage we get from the SDK on Cloudflare.

When Next.js apps are deployed to Cloudflare Workers via OpenNext, the Sentry SDK now correctly reports cloudflare as the runtime instead of node or vercel-edge.

e2e tests still failing cry

[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	8,999	-	8,725	+3%
GET With Sentry	1,665	19%	1,664	+0%
GET With Sentry (error only)	5,997	67%	6,107	-2%
POST Baseline	1,167	-	1,193	-2%
POST With Sentry	570	49%	597	-5%
POST With Sentry (error only)	1,032	88%	1,037	-0%
MYSQL Baseline	3,207	-	3,234	-1%
MYSQL With Sentry	394	12%	443	-11%
MYSQL With Sentry (error only)	2,619	82%	2,624	-0%

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