chore: update default db to prisma postgres

[ankur-arch]

Summary

This PR updates our /orm examples to use Prisma Postgres instead of SQLite.

Changes

• README Updates:

  • Instructs users to run npx prisma@latest init --db.
  • Adds guidance on seeding the database.
  • Provides steps to remove the Accelerate extension when using providers other than Postgres.

• Code Updates:

  • Converts fluent API queries to standard function calls. Also updated READMEs accordingly.
  • Adds instructions for extending the Prisma Client in NestJS applications in README, also updating the application code.
  • Modifies tests to run sequentially (using a single database URL) instead of in parallel. See discussion for additional context.

Exclusions:

• /orm/nuxt-module-prisma: No changes made since it’s tied to the guide [here](https://www.prisma.io/docs/orm/more/help-and-troubleshooting/prisma-nuxt-module).
• /orm/postgis-express: No updates were applied as this example does not use Prisma Postgres. I encountered issues getting it to work and decided to prioritize the other examples.
• Product examples for Optimize, Accelerate, Pulse.