feat: make pglite default for generate without requiring external postgres

[iprasen]

Overview

Fixes #2.

Claims Algora bounty:
@algora-pbc /claim #2

Problem

Previously, running bun run db:generate or pgstrap generate defaulted to connecting to an external PostgreSQL instance unless --pglite was explicitly supplied. When running in environments without PostgreSQL running in the background, type generation failed.

Solution

1. Default pglite to true in generate():
   • generate() now defaults to pglite = true, running migrations in a temporary in-memory PGlite instance and dumping structure without requiring external PostgreSQL.
2. Default CLI option pglite to true:
   • Running pgstrap generate (and thus bun run db:generate) works immediately out of the box.
   • External Postgres users can opt out via pgstrap generate --no-pglite.
3. Lifecycle & Environment Variable Cleanup:
   • Wrapped PGlite socket server generation in a try ... finally block so that server.close(), PGlite disposal, and process.env.DATABASE_URL restoration always run even if type generation or tree dumping fails.
4. CLI Handler Async Safety:
   • await generate(...) in the CLI action handler to ensure errors are propagated and asynchronous execution finishes before exiting.
   • Added ESM/CJS compatibility for the CLI invocation.
5. Testing:
   • Added unit and integration tests for:
     • generate defaulting to PGlite when the option is omitted.
     • generate opting out to external Postgres when pglite: false.
     • DATABASE_URL restoration and socket server cleanup when errors occur.

[iprasen]

@algora-pbc /claim #2