[codex] Add transaction helpers

[zth]

Summary

Adds small ReScript transaction helpers for the existing pg bindings:

• Pg.Client.transaction(client, callback) sends BEGIN, runs the callback, commits on success, and rolls back/rethrows on failure.
• Pg.Pool.transaction(pool, callback) checks out a client, delegates to Client.transaction, and releases the client on both success and failure.
• Includes the generated src/res/PgTyped.js runtime sibling required by the example test runtime.
• Documents transaction usage in RESCRIPT.md.
• Adds example coverage for rollback behavior and pool client release.

Refs #2.
Supersedes #27.

Validation

• npm run build
• npm test --workspace packages/cli -- --runInBand
• npm run lint -- --project packages/cli/tsconfig.json
• npm run build --workspace packages/example
• node -e "require('./packages/cli/src/res/PgTyped.js'); console.log('ok')"

I also attempted npm test --workspace packages/example, but the Docker run is blocked locally on Apple Silicon: the container reports Package @rescript/linux-x64 not found during typegen and then the follow-up test container waits on Postgres. I stopped and cleaned up the compose containers with docker compose down --remove-orphans.

[zth]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: e72fb0c02d

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[zth]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

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[zth]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

ℹ️ About Codex in GitHub

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