fix(types): type pg Client as the constructor (typeof Pg.Client)

[imharjot]

What

Change the Client member of the public PostgresDb type from Pg.Client to typeof Pg.Client.

Why

At runtime the plugin assigns the pg Client class (the constructor) to app.pg.Client:

// index.js
const db = {
  connect: pool.connect.bind(pool),
  pool,
  Client: pg.Client, // <- the constructor/class, not an instance
  query: pool.query.bind(pool),
  transact: transact.bind(pool)
}

But the type declaration described it as an instance:

// index.d.ts (before)
export type PostgresDb = {
  pool: Pg.Pool;
  Client: Pg.Client; // instance type
  ...
}

Since @types/pg declares export class Client, Pg.Client is the instance type and typeof Pg.Client is the constructor type. As a result, instantiating a one-off client via the decorator — new app.pg.Client({ connectionString }) — failed to type-check:

error TS2351: This expression is not constructable.
  Type 'Client' has no construct signatures.

even though it works at runtime.

Change

// index.d.ts (after)
Client: typeof Pg.Client;

and the corresponding type test now asserts the constructor type:

expect(app.pg.Client).type.toBe<typeof Client>()

Testing

• npm run test:typescript (tstyche): all 4 type-test files pass, 13/13 assertions pass.
• npm run lint: clean.
• Verified new app.pg.Client({ connectionString }) now type-checks (no TS2351), and reproduced the failure before the change.

This is a type-only change with no runtime impact, so unit-test coverage (c8 --100) is unaffected.