feat(db-vercel-postgres): migrate from deprecated @vercel/postgres to successor @neondatabase/serverless

[siimsams]

What?

Migrates db-vercel-postgres from the deprecated @vercel/postgres package to @neondatabase/serverless.

Why?

@vercel/postgres has been deprecated and is no longer maintained. All Vercel Postgres stores have been migrated to Neon's native integration.

On top of that, its VercelPool extends @neondatabase/serverless's Pool (not pg's), which is incompatible with drizzle-orm@0.45.2's stricter NodePgClient type — so continuing to depend on @vercel/postgres forces type-casting workarounds.

How?

• Replace @vercel/postgres with @neondatabase/serverless in packages/db-vercel-postgres.
• Use drizzle-orm/neon-serverless for remote Neon connections and keep drizzle-orm/node-postgres for local connections (localhost / 127.0.0.1).
• Update VercelPostgresAdapter types to reference @neondatabase/serverless's Pool / PoolConfig and NeonDatabase, and refresh the related JSDoc.

Fixes #13404

Extracted from: #16168