createBrowserContext should not create the default browsercontext

Issue discovered here: https://github.com/lightpanda-io/browser/pull/777#discussion_r2149411411

From puppeteer, without calling `createBrowserContext`, the `defaultBrowserContext` already exist. This works for LightPanda already.
Calling create should not return the same context-id as the default browsercontext as revealed in the linked discussion.