database transaction support in typescript

[fredr]

Adds support for transactions in runtimes/core and runtimes/js

We should probably merge encoredev/rust-postgres#1 and update Cargo.toml again. (suggested that change upstream as well sfackler/rust-postgres#1230)

[encore-cla]

All committers have signed the CLA.

[Copilot]

Pull Request Overview

This PR adds support for database transactions in both the JavaScript and Rust runtimes. Key changes include:

• Introducing transaction methods (begin, commit, rollback, and savepoint) in the JavaScript bindings.
• Implementing the Rust-side transaction logic and exposing it via the core SQLDB modules.
• Updating Cargo.toml to use a different branch for tokio-postgres and postgres-protocol.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
runtimes/js/src/sqldb.rs	Adds transaction support with new async methods (begin, commit, rollback, savepoint) in the SQLDatabase API.
runtimes/js/encore.dev/storage/sqldb/database.ts	Revises the database API to integrate transactions and improve documentation.
runtimes/core/src/sqldb/transaction.rs	Introduces the Rust implementation for transactions including transaction lifecycle management.
runtimes/core/src/sqldb/mod.rs	Exposes the new transaction module in the core SQLDB module.
runtimes/core/src/sqldb/client.rs	Updates the client API to support beginning new transactions.
Cargo.toml	Updates dependency branches for tokio-postgres and postgres-protocol.

Comments suppressed due to low confidence (1)

runtimes/js/src/sqldb.rs:173

• [nitpick] Consider refactoring this pattern to avoid the explicit use of deref_mut() for improved readability; matching directly on the locked Option may be clearer.

if let Some(ref mut tx) = self.tx.lock().await.deref_mut() {