fix: use pg-protocol CommonJS entrypoint

[zfaustk]

Fixes #3700.

Problem

When the Cloudflare Vitest/Vite worker pipeline inlines both pg and pg-protocol, the CommonJS pg entry can resolve the bare pg-protocol import through its ESM condition. Loading that ESM wrapper from pg's CommonJS files then fails before any tests run:

SyntaxError: Cannot use import statement outside a module
at pg/lib/connection.js?mf_vitest_no_cjs_esm_shim:5:30

I reproduced this with the standalone fixture from #3700 using released pg@8.23.0, pg-protocol@1.16.0, @cloudflare/vitest-pool-workers@0.16.18, and Vitest 4.1.9.

Fix

• load pg-protocol/dist/index.js explicitly from pg's two CommonJS entry files;
• add a unit regression that verifies the subpath is exported and both call sites keep using it.

This remains package-manager independent: pg-protocol exposes ./dist/*.js through its public exports map, and pg currently depends on pg-protocol ^1.16.0.

Tests

• published standalone worker fixture: fails before the patch, passes 1/1 after it;
• make test-unit from packages/pg;
• yarn lint;
• yarn build;
• Prettier check for all changed files;
• git diff --check.

The full PostgreSQL/Node matrix was not run locally; it is left to CI. The repository's existing Cloudflare integration test also gets past module collection with the worker inline settings after the patch, then stops at this executor's unavailable PostgreSQL endpoint.

Implementation and test preparation were assisted by Codex. The reproduction and all reported checks above were run against this branch.

[charmander]

This seems like a build misconfiguration, not a pg issue that should be fixed by changing the imports in this way.

[zfaustk]

Thanks — agreed. The reproduction showed the worker build selecting the ESM
condition for a CommonJS caller, but changing pg's imports fixes that at the
wrong layer. I'll take this out of review and investigate the Vite/Workers
configuration instead.