feat: TS support improvements

[SebastianSedzik]

Enhanced TypeScript support:

• constrained the @suite decorator to class contexts only.
• constrained the @test decorator to class method context only. Type check of test method arguments.
• exported the TestArgs type to provide validity within test methods.

import { suite, test, TestArgs } from 'playwright-decorators';

@suite()
class ExampleSuite {
  @test()
  async exampleTest({ page }: TestArgs) { // <- TestArgs ensures correct types of arguments
    // ...
 }
}