Symbol.asyncDispose support

I propose support AsyncDisposable on postgres.Sql (https://github.com/tc39/proposal-explicit-resource-management) so that developers can opt-into ending the connection automatically at the end of the current scope.

before

import postgres from "postgres";

const sql = postgres();

const result = await sql`SELECT * FROM some_table`;

console.log(result);

await sql.end();

after

import postgres from "postgres";

await using sql = postgres();

const result = await sql`SELECT * FROM some_table`;

console.log(result);

Start at the postgres.Sql API and compare its current connection lifecycle with the TC39 Explicit Resource Management proposal. Verify that await using sql = postgres() supports Symbol.asyncDispose and closes the connection with the same effect as await sql.end(); the issue provides no file or test path, so locate the existing lifecycle tests first.