Allow interface and empty interfaces in .d.ts files

[matejchalk]

It is common to use .d.ts files to extend some shared TypeScript interface like Window. For example, extending matchers in Vitest requires creating a vitest.d.ts as follows:

/* eslint-disable @typescript-eslint/consistent-type-definitions,@typescript-eslint/no-empty-interface */
import type {
  CustomAsymmetricPathMatchers,
  CustomPathMatchers,
} from './lib/extend/path.matcher.js';

declare module 'vitest' {
  interface Assertion extends CustomPathMatchers {}
  interface AsymmetricMatchersContaining extends CustomAsymmetricPathMatchers {}
}

It isn't possible to achieve this with types instead of interfaces, and the empty object is also valid in such cases.

Acceptance criteria

• disable @typescript-eslint/consistent-type-definitions for **/*.d.ts files
• replace @typescript-eslint/no-empty-interface with @typescript-eslint/no-empty-object-type, and disable it for **/*.d.ts files